Sadistic Choice: It happened many times. Often Baron Ashura held someone hostage and threatened with to kill him or her if Kouji did not surrender, but there were different instances:
In episode 17, Dr. Hell crafted a Mechanical Beast could set earthquakes off. After using it to bring down several Japanese cities, Baron Ashura threatened with obliterating Tokyo unless Dr. Hell was appointed director of Photonic Research Institute. If the heroes gave in, Dr. Hell would have full and unopposed access and control to the lodes the Japanium was extracted from and plans to build his own Photon Atomic engines, and nobody would be able to stop him from taking over the world. If they did not agree, Tokyo would become a giant hole in the ground.
In episode 18, a Mechanical Monster cuts a passenger ship in half. A woman reaches a lifeboat but her mother has been caught in one of the whirlpools formed by the sinking ship. If she stays away, her mother will die. If she comes closer, maybe both of them will die. At the end her mother chose for her. She shoved the boat away her. She drowned, but she managed to save her daughter's life.
In episode 31, Dr. Hell kidnapped three men, hypnotized them in piloting three of his Mechanical Beasts and ordered them to attack Mazinger-Z. Thus, Kouji found himself severely limited, since if he attacked full-force, the prisoners could die.
In episode 61, Lorelei, a little girl his little brother was infatuated with, fused with a Robeast and challenged Mazinger-Z. She could not be split from the robot, and if Kouji fought, he would kill her and would break his brother's heart. Finally Kouji had to fight, and Lorelei died.
In the original myths Hades was the God of Underworld, his default shape was humanoid (but like all Greek deities he was a shape-shifter), and even though he was not exactly a nice guy, he was not worse than his relatives. In the Mazinverse he is a God of Evil whose (unchangeable) shape is that of a giant being of fire and wishes conquering the surface world.
Scooby-Doo Hoax: In one anime episode, the heroes got reports of a huge, aquatic monster living on a chain of lakes near from Mount Fuji. When Kouji went to investigate to the site, a witch appeared all of sudden and warned him the lake monster would curse him if he did not leave. That woman had been scaring away whoever came to investigate the monster sightings. It did not take long for Kouji to discover that witch was Baron Ashura in disguise and the monster was a Mechanical Beast (Granada E3). Baron Ashura was using the curse hoax to hide their activities (mining the lakebed for uranium to fabricate nuclear bombs).
In one manga chapter, Kouji and his friends go to a hot springs resort. However, the area is apparently being haunted by ghosts. Boss is terrified but Kouji does not believe one word of it, so he and Sayaka set to investigate what is happening. Quickly they discover the ghosts in reality are androids commanded by Count Brocken, one of the Co-Dragons of Dr. Hell.
Sea Mine: In episode 22, Baron Ashura used electric sea mines -called Balanger M1-. They were light blue with dark blue spikes that covered its bodies, and they were able to move through water and home in on an opponent. Once they came into contact, they released electric charges to hurt their target. That episode also featured Mechanical Beast Balanger M2, a giant robot capable to transform into a red, spiky, electric sea mine.
Sea Monster: The Dragonosaurus from a Crossover movie. It was a very bizarre monster: its body was a amorphous, red-and-black blob with a face. Several long, snake-like creasted heads sprouted from it.
Selective Magnetism: Mechanical Beast Bazil F7 was armed with magnetically-charged armor plates that could be detached off its body and launched at its adversary (with the purpose of sticking to it and disrupting their mechanisms). However the magnets did not attract other objects when they were working, and they stuck to Mazinger-Z and Aphrodite-A in spite of they are not made of steel to begin with.
Sayaka / Boss: Early on Boss was very infatuated with Sayaka who was totally smitten with Kouji. However, Sayaka's reaction during one of the finalr arcs of the manga suggests maybe Boss had one chance... but he did not take it. So he cared no longer or he valued his friendship with Kouji too for trying anything with Sayaka.
Kouji / Erika: Erika was a enigmatic, amnesiac girl showed up one day in the Institute. There was a certain chemistry between Koui and her... but it went nowhere since it was revealed she was anandroid. And then she got murdered.
The original Go NagaiMazinger Z manga had way more Ship Tease between Kouji and Sayaka than the anime adaptation. Thus, when Sayaka told Kouji he was being transfered to her high-school (in the early chapters), he blushed and stated he "would look forward to it".
And when Boss got a crush on a teacher, Kouji was glad because then he "would have no competition for Sayaka's heart".
And then you have the Hot Springs Episode. Kouji and Sayaka accidentally see each other naked in the springs, run away and collide with each other (they were so started they did not realize the spring was circular and they were running into circles). Kouji helped Sayaka on her feet, and after a row of mutual apologies they bathed together, back-to-back and with huge blushes on their faces. That scene doubled like both a CMOF and a CMOH, and it was adapted in a Shin Mazinger episode.
In the anime had less teasing moments but they definitely were there, although often in the way of Belligerent Sexual Tension. In episode 7, Shiro is praising Boss for being the Only Sane Man in that episode, and Boss is getting smug... until one of his goons suggest him noticing Kouji and Sayaka are walking away together. Boss got quickly angry.
In episode 29, Kouji sees a Mechanical Beast -Grengus C3- walking from the place where Aphrodite A had gone to a while ago, and he... completely freaks out. He hops on the first bike he finds -not realizing it was not his- and drives towards the place the Beast came from, screaming "SAYAKA!" the whole way. When he found her, she was lying on the ground, knocked out. He managed to wake her up and then he hugged her silently.
And in episode 32 they are having their... third or fourth fight in that episode. Meanwhile, Shiro is fortune-telling and he tells "It is funny. The cards tell they are destined to be together forever."
Episode 48, Sayaka and Boss are getting fun teasing a disgruntled Kouji at the end of the episode. Then Sayaka asked Boss going out to have lunch. Kouji flipped instantly, getting jealousy and shouting "What is going between them?"
In episode 52 Kouji and Sayaka have their bigger fight. Kouji gets badly wounded after sortying alone, and Sayaka kisses him while he is sleeping in a hospital bed. Later Kouji is bleeding on the ground, unconscious and maybe dead and Sayaka makes an Anguished Declaration of Love ("Please, don't die. I want getting married to you). Then he opens his eyes, smiles and replies he is not going to get married to a tomboy. Sayaka roars and she decides killing him for real.
And then you have all times Sayaka got jealousy when a girl (even if she was non-human!) got close to Kouji: Minerva, Misato, Erika...
Their last scene in episode 92 went they flying together to America, and smiling at each other.
In the Gosaku Ota alternate manga adapted that scene, though, they DID kiss. And it was glorious (they were floating in a void, and flower petals fell around them).
In that same alternate universe, after that scene their relationship got uneasy for a while since Kouji, unsure of how dealing with it, was avoiding her, and Sayaka got saddened because he was distancing from her. However, at the final scene, the group meets Kouji again and he reveals he has been turned into a cyborg due to his body becoming badly harmed during the Final Battle. He says Sayaka he's sorry because he no longer is human... and her reaction was hugging him and telling she does not care, and he is still her Kouji.
Again in that universe, Boss kissed an unconscious and bedridden Sayaka before leaving for a seemingly unwinnable battle, telling that all he could make for the girl he loved was dying like an hero.
And in the Great MazingerGosaku Ota manga, when Kouji and Sayaka returned from America, Tetsuya teased Kouji, asking what he had done with Sayaka during their stay overseas. Kouji blushed.
Talking about Tetsuya, there was a healthy amount of teasing between Jun and him. Jun flirting with an Oblivious to Love Tetsuya, Jun pretending a sprained ankle just so Tetsuya rubbed her foot (unfortunately it did not work like she hoped), Tetsuya returning the unwanted gifts of a Stalker with a Crush in person and warning that Jun wanted being left alone, he getting jealousy and accusing her of wanting to replace him with Kouji (and being slapped for it. Seriously, it was stupid)... And in the Go Nagai manga a War Beast got Jun hostage. Cue Great Mazinger beheading the Beast with a brutal kick as Tetsuya yelled she was a very special person for him.
Teasing between Boss and both female leads (Sayaka and Jun) revolved around Boss being a Stalker with a Crush and both girls ignoring or pretending not noticing his poor attempts. However, sometimes you got them standing up to him when Kouji or Tetsuya were acting stupid.
In UFO Robo Grendizer there was a good amount of teasing between Duke and Hikaru. Many scenes featured them together, sometimes at night, invoking the ire of Hikaru's Overprotective Dad who threatened with hanging Duke with his bare hands if he gets closer to his daughter (Not Hyperbole). And in the UFO Robo Grendizer versus Great Mazinger feature, Goro teases his big sister and Duke are in love.
There also was Belligerent Sexual Tension between Kouji and Maria (interesting, considering Sayaka was meant to be newest team member and Maria replaced her due to Executive Meddling, filling her role). In a scene, Kouji tries to wake up an unconscious Maria using [CPR], and then Maria woke up suddenly and slapped him.
Sayaka and Maria use to fight over Kouji in universes where they interact, like the Super Robot Wars games or the Dynamic Heroes e-manga. In the final scene, the whole cast are giving goodbye to Duke and Maria. Then smirking Sayaka suddenly snuggles up Kouji, and Maria goes ballistic.
In Mazinkaiser twins Loru and Lori ask Kouji if he is in love with Sayaka, and he starts stuttering.
And in the Mazinkaiser manga, Sayaka stops the rampage of a berserk Mazinkaiser by huging the Humongous Mecha with her own Fem Bot... Kouji felt like if a naked Sayaka was hugging him from behind -and he was naked, too-, and then he snapped out of his trance.
The Ship Tease between Kouji and Sayaka got cranked up in Shin Mazinger Zero. At the first arc they were a couple. In the next timeline/arc, Sayaka blushes when Kouji explains he can't tell why, but he is crying because he has seen she is fine. Sayaka gets jealousy when she sees girls getting too close to Kouji, Minerva states Sayaka is irreplaceable for Kouji...
Shirtless Scene: Kouji Kabuto pulled this sometimes, specially late in the series (the episode where Erika showed up comes to mind). Dr. Hell also pulled this at the end of Mazinkaiser for seemingly no reason, and despite being a very old man.
Shooting Superman: Whenever a human army turns on Mazinger-Z, Great Mazinger or Grendizer, they always shot round after of round of ammo in spite of they should already know conventional weaponry not even scratches them (it was kind of subverted the first time Mazinger-Z was activated in the manga. The army could not know what that Humongous Mecha was made of. And in that time, the dome protected Kouji inside the cockpit was still open, so the pilot was still vulnerable. Shooting Superman in that situation could have worked). Also, when a Robeast appears, the army insists on attacking them in spite of they should know after the first few times they are wasting ammo, men and money. It was kind of subverted in a Mazinger-Z episode, though: a squad of Iron Masks surrounded Aphrodite-A and threw a hail of spears against the Fem Bot. They very obviously did not damage it, but they managed to slow Sayaka down (they were so many they were very distracting) what was their intention.
Short-Range Long-Range Weapon: Mostly it averted the trope. Usually both the Mechanical Beasts equiped with long range weapons (beams, bolts, missile launchers, machine guns) and Mazinger-Z avoided getting close each other often they had to. Some Beasts even made a point of this (Jenova M9 was a robotical snipper. Coming near the enemy would be the last thing it would do). There were exceptions: Sometimes Beasts got over-confident and got close (like Kingdam X10. When Mazinger -apparently- ran out of power and fell face-down, Kingdam dissipated its mirage trick and approached to skewer it wth its sword instead of keeping blasting the robot with lightning bolts. Bad idea). And in the original manga, Kouji prefered fighting with punches and kicks, using his robot's long-range weapons to finish their enemies off.
Shoulder Cannon: Several Mechanical Beasts were equipped with them. Examples were Winder A2 or the ninja siblings Blazas S1 and S2. Their shoulders were fitted with missile launchers.
Sibling Rivalry: Kouji and Tetsuya Tsurugi were a pretty tragic example. Tetsuya was adoptive son of Kenzo Kabuto's, Kouji biological father. When Kenzo got reunited with Kouji in Great Mazinger, Tetsuya -who had a TON of abandonment and self-confidence issues- thought his father would forget about him now his son by blood was back. He got very jealous and argued and fought with Kouji about anything and everything, determined to prove to their father that he was the better than Kouji. Unfortunately, his jealousy and his bickering caused Kenzo's death. He suffered a Freak Out cause it.
Sibling Team: Kouji and his adoptive brother, Tetsuya. When they are actually fighting their enemy instead of each other, they are virtually unstoppable.
Silly Rabbit, Idealism Is for Kids!: In a story arc of the Gosaku Ota manga alternate continuity Baron Ashura manages kidnapping Kouji and tries to talking Kouji in joining him (or her. It. Whatever). When Kouji refuses, Ashura goes in a What Is Evil? rant, stating "justice" and "peace" are only meaningless, empty words invented by people because they are too coward and weak to accept the truth (Might Makes Right according him) and protect themselves, and then he taunts Kouji telling the only thing his idealism has got him are troubles and humilliations.
A Simple Plan: In episode 46 Dr. Hell's had a pretty simple plan: send two Mecha-Mooks to infiltrate into the Institute and planting several nukes in Mazinger-Z's pool. Everything explodes, he wins. However that simple plan met due to his Kikaijuu and his troops running into abandoned babies, suicidal mothers, and at a point they got involved in a manhunt through a woodland.
Sinister Scythe: Several Mechanical Beasts were armed with scythes: Garada K7 (two scythe blades were mounted on its skull and they could be used like boomerangs or like weapons in hand-to-hand combat), Brutus M3 (one sctyhe replaced its right arm), Karma K5 (it was armed with a more normal-looking)...
Sizeshifter: Several Mechanical Beasts had the ability to changing size. The first of them -Bicong O9- showed up as soon as episode 12. Subverted with Double Faizer Dr. Hell's strategy was deceiving the enemy in believing Faizer was a size-shifter, but in reality they were two Beasts: a large and a tiny one.
Sliding Scale of Idealism Versus Cynicism: Even though they have plenty instances of dark, cynical moments, Mazinger Z and its sequels fall firmly into the idealistic side. When push came to shove, it was through courage, guts, faith and The Power of Friendship the heroes and heroines managed to prevail.
Small Name, Big Ego: Boss thinks he is the smartest and biggest Badass ever, the best biker around and a real ladies man, and people would pay for the chance to attend his birthday party (not joke. In episode 20 He tried to have his classmates paying for tickets. And he was shocked when all girls ran away from him screaming). Everyone else knows he is the Butt Monkey. Hence, when Kouji showed up, showing he was a real Badass, and a better biker and getting all girls -especially Sayaka- crazy over him right away, Boss understandably was not happy, and he constantly tried to showing Kouji up with very little success. He went so far to build his own -goofy-looking- Humongous Mecha using metal scraps and junk from a rubbish dump, and claimed it would replace Mazinger-Z itself. Tip: It did not.
Small Reference Pools: This is one of the few Humongous Mecha shows general anime fans have heard about, at least. And depending on the country, you can make references to it expecting people will quickly catch on (in Spain it is still the most popular Super Robot show. Mention Mazinger Z and nearly everyone will know what you are talking about).
The Smurfette Principle: Sayaka Yumi was the only female main character (albeit, unlike other Smurfettes, she demanded being taken seriously like her own individual) and the only recurring female character until Misato appeared in the last season. Between the bad guys, Baron Ashura may or may not count like female character. Dr. Hell mostly "hired" males (let's think of it, it can be infered from his backstory he had actually come to loathe women), but every so often he made Robot Girls or female androids Minerva, Erika, the Gamia triplets, the robots impersonated Hitomi and Kouji and Shiro's mother...)
Sniping the Cockpit: In the Mazinger trilogy aiming for the cockpit (clearly visible in Mazinger-Z and Great Mazinger) is a common tactic constantly employed by Genre Savvy villains... and the army when the Government turns on the heroes (which also is an alarmingly common occurrence). In fact, it happened in the first Mazinger-Z manga chapter (Mazinger went on a rampage due to Kouji thinking Falling into the Cockpit was a good idea. Several tanks attacked Mazinger, deliberately aiming for the cockpit). And in a Great Mazinger manga episode, a Warbeast is holding Great Mazinger still as Marquis Janus orders to snipe the cockpit. However, the likewise Genre SavvyHumongous Mecha builders had the cockpits specially reinforced to protect the pilot.
The Social Darwinist: Baron Ashura is a type four who uses the "survival of the fitest" like an excuse/justification to make whatever he wants. In a story arc of the Gosaku Ota manga alternate continuity Baron Ashura manages kidnapping Kouji and tries to talking Kouji in joining him (or her. It. Whatever). When Kouji retorts he has no interest in becoming a criminal, Ashura goes in a What Is Evil?Might Makes Right angry rant, uttering that in the nature the weak succumbs to the will of the strong and the strong survives. That is how the world always did, does and will work, and "good", "bad", "peace", "justice"... are meaningless, empty words.
Speech-Impaired Animal: Bakarasu was a raven ("Bakarasu" roughly means "Dumb crow") Boss and his gang used as a lookout or a messenger. In return, Bakarasu mocked Boss, annoyed him and drove him mad. Bakarasu strangely could talk -and laugh, usually at Boss-, and theoretically it worked alongside Boss, Nuke and Mucha, but in reality it did whatever it pleased. It only had one appearance in Mazinger Z (episode 69), but he showed up in several Great Mazinger episodes.
Spell My Name with an "S" (Notable for managing to largely avoid this, outside the twin blonde research assistants. Rori, Loli, Lori, Roli? Roru, Lolu, Rolu, Loru, or possibly Roll? Nobody knows for sure.)
Spin Attack: A variant. Mazinger Z possess a technique called Daisharin Rocket Punch ("Giant Swing Rocket Punch"). Rather spinning its whole body,the Humongous Mecha spins its arms rapidly, building up momentum before firing off both fists in standard Rocket Punch fashion.
Several Mechanical Beasts had spin attacks: Goronko S2 spun around and then rammed the enemy; Spartan K5 whirled its trident very, very rapidly to create a twister capable pick even a Humongous Mecha; Balkan P5 expelled air out of ducts all over its legs and spun around to wrap itself into a tornado; Grengus C3 wrapped its enemy in chains and then it spun around, dragging its enemy with it before slamming it in the ground...
Spot the Imposter: In a episode Dr. Hell fabricated a robot seemed just like Prof. Yumi. However it was quickly identified by Sayaka when she noticed the imposter's nails were black. Dr. Hell used that strategy more times, creating a robot looked right like a secondary character and even going as far as building a robot resembled The Hero Kouji. They also were spotted sooner or later.
That plot was partially reused in a Mazinkaiser episode. The Dragon Baron Ashura kidnapped Prof. Yumi and disguised like him. Sayaka suspected from him nearly right away, though, because he tossed into a trash bin a birthday gift, and she told her father would never do that.
Stacy's Mom: Misato, Boss' cousin. She is a professional copter pilot in her early twenties and all male teens (including The Hero Kouji) other than her cousin are infatuated with her. She also showed up in one of the manga versions of Great Mazinger, and Tetsuya also felt attracted to her.
Shiro and Lorelei. Lorelei was a Robot Girl built by a scientist wanted to prove he was better than Dr. Kabuto, builder of Mazinger-Z. He built an Humongous Mecha -Rhine X1-, and a Robot Girl -Lorelei- was meant to fuse with it to make it work. When her father got a fatal wound, he confessed the truth to her and pleaded her to defeat Mazinger. Determined to fullfil her father's last will, she merged with Rhine and challenged Mazinger to a death match. Kouji was forced to fight and kill her. Shiro was devastated after that.
Minerva-X and Mazinger-Z itself also are an example. Minerva-X was a Fem Bot designed by Dr. Kabuto especifically to be Mazinger-Z's Battle Couple. Unlike Mazinger, though, she was a robot capable to think and feel emotions like an human being, and she was in love with Mazinger-Z. However, Dr. Kabuto never got around to build it. Unfortunately, Dr. Hell got his hands on the plans and built her to destroy Mazinger-Z. However, Minerva-X got rid from his control and refused fighting Mazinger-Z, so he decided to destroy her. Their condition of Star-Crossed Lovers not only comes from this but also it comes from Mazinger-Z IS a machine and it can not reciprocate her feelings.
The Starscream: Two Dr. Hell's servants fit the trope: Viscount Pygman and Archduke Gorgon. The former disobeyed orders the whole time and finally betrayed his creator, taking over the Institute on his own and refusing handed over the control of it to Hell (He earns brownie points, though, for being the only Dr. Hell's henchmen showed some spine in front of Gorgon). The later allied himself with Hell but spend the whole time insulting and scorning Hell and his henchmen, undermining his authority and scheming to overthrow Hell at the first chance. He was sucessful. Gorgon subverted the trope slightly since he was not planning replacing Hell with himself but with the Emperor of Darkness.
Start of Darkness: Hell's mind was already unstable and unsound cause his upbringing. However, when he found out the woman he loved was in love with another man Juzo Kabuto, future builder of Mazinger-Z and Kouji's grandfather, he... flipped out and attempted to murder his perceived rival. It then went From Bad to Worse. Shortly after he tried helping someone... and he got the crap beaten out of him for it. Later he was crawling back towards his home, bruised and blood-stained, muttering "Mediocre imbeciles! You don't deserve being alive! One day I'll purge the world off all of you! And then everybody will have kneel before me". When you heard his words and saw his utterly mad stare you realized he had snapped out completely and Dr. Hell had been born.
The Stations of the Canon: Dr. Hell's surfacing, Dr. Kabuto's death, Kouji finding Mazinger and trying piloting for first time with disastrous results, Sayaka showing up to save him from himself, Baron Ashura attacking the institute, first meeting with Boss... To spice things up, some Fanfic writers try blending or playing out of order several minor events and battles.
A classic instance is episode 8, when Kouji voted against a proposal to turn Aphrodite-A into a combat-capable mecha, telling he needed no help. And when Sayaka argued with him he told she was an idiot did not get that girls must not fight.
Stealth Sequel: Shin Mazinger Zero seemed an alternate universe or retelling of the original series... until Kouji starts to have visions of events that happened in the original show, including a flashback of the death of Minerva-X, and it is revealed that Shin Mazinger Zero is a sequel to the original anime, in the which the characters are locked in a perpetual time loop.
Stock Ninja Weaponry: Blazas S1 and S2 -two Mechanical Beast showed up in episode 46- used shuriken and kunai like weapons.
Stock Shout-Outs: This series gave us the Super Alloy Z and the Rocket Punch. They pop up frequently, especially the second, which has quickly became THE most famous and most ubiquitous Super Robot weapon, showing up in all kind of works. Whenever a character screams "Roketto Panchi!" it is directly referencing the Trope Namer.
Since Spaniards Love Mazinger-Z, the Spanish Dub Name Change variant ("¡Puños Fuera!", meaning "Fists Out!") has become so omnipresent that it has been used in movie titles. And when a foreign work features a Rocket Punch, whatever attack name that the character screams is automatically replaced by "¡Puños Fuera!" more often than not.
Super Spit: Many Beasts could spit gallons of acid, poison and other corrosive fluids. Sometimes it was a kind of gluey substance to paralyze or hinder the enemy. Examples abound: Mechanical Beasts Baras-K9, Gusios-β3...
Super Prototype: averted. Mazinger Z was lacking a lot of its special features at first and regularly had to be upgraded and re-outfitted with new equipment. As it turns out, the realSuper Prototype is MazinKaiser...
Averted throughout the OVA, though. Shin Great Mazinger and Mazinkaiser are explicitly stated to be the finished models, their predecessors are the prototypes.
Super Robot: May not have started, but certainly defined and named the genre.
In a number of Super Robot Wars games you can convince Minerva X to join your team. At least 2, 2G, Compact 1, and Advance, although in 2 she only joins temporarily and in Advance she 'dies' and you have to assign an actual pilot to the robot.
Super Villain Lair: Dr. Hell had TWO: the island of Bardos, where he found the Mykene Humongous Mecha, and the -properly named- island of Hell, an islet near from Japan where he moved to at the second half of the series. His first base looked like a deserted island, covered with ancient, half-crumbled ruins, but his second fortress seemed less ordinary, featuring a mountain with four gigantic faces carved on the slopes. Nonetheless, both of them included:
And in the original manga, his second fortress could transform into a humongous Humongous Mecha. And in the Gosaku Ota episodes, he could launch it off to the space and blow it up (in case his enemies invaded his island and he could not win).
Surrounded by Idiots: Dr. Hell often feels like this -and rightfully so-. When he was young it was because he thought he was smarter than anybody, but now it is because his minions are, well, stupids. In an episode he invokes the trope almost word by word. His Co-Dragons have been fighting for the whole episode, even when they were supposed to engage the enemy. At the beginning he had tried to stop them and force them to cooperate, but it did not work. So during their latest fight he is -unsuccesfully- trying to ignore them as he has dinner, and he grumbles he is surrounded by idiots.
Dr. Hell: Why, oh, why such a genius as myself is surrounded by idiots?
Tail Slap: Several Mechanical Beasts (such like Danchel or Deltan V8) were endowed with powerful tails, capable to hit or coil around the enemy and strangle it. Often they had some weapon attached or shot missiles, acid or poison.
Take Over the World: According his Backstory revealed in one of the manga versions, Dr. Hell was abused and belittled by everyone when he was a child until his mind snapped and he decided he wanted to make all pay: he would purge the world off idiots and force everybody to bow down to him. During the rise of Hitler, he realized if he took over the world he COULD do just that. Over ten years after the World War II he finally found the means as he researched several ancient ruins.
Tap on the Head: Boss used the "low blow to the solar plexus" variant with Kouji to try to avoid he fought against the Mykene Warrior Monsters in the last episode. Maybe it was used in a more realistic way than usual, though, since when Kouji regained consciousness shortly after, he seemed being in pain.
A Taste of Power: In the first dozen episodes, the Mechanical Beasts can barely even scratch Mazinger-Z, let alone threaten it. They were too weak, their weapons not powerful enough, and the battles wer over as soon as Kouji managed to connect several consecutive attacks. The only reason that Kouji struggled during that time was he was still trying to learn how piloting Mazinger. When Spartan K5 -a Gladiator-like Beast single-handily beat the crap out of Mazinger as easily as it was shrugging all its weapons off- showed up in episode 14, it was a wake-up call of playtime was over and Big Bad Dr. Hell was at last stepping up his challenge.
Technician Versus Performer: Koji and Tetsuya have distinct ways to pilot their respective Humongous Mecha. Kouji is the Technician, who uses his weapons in a normal way -such as Mazinger's Photon-powered Eye Beam as a long range weapon-, combining them with pure brute force and Combat Pragmatism. Tetsuya is the performer who combines his own Combat Pragmatism by using Great's wide arsenal of weapons in an unorthodox way -such as shooting Thunder Break with both weapons or using it to turning his swords into Lightning rods, his surprisingly weird way of handling swords, or covering Great with Breast Burn heat energy (a movement which later would be adapted in Super Robot Wars Alpha and turned into Mazinkaisers Kaiser Nova).
In the manga version of the battle versus Jinray S1, Professor Yumi explains Jinray's electrical discharges generate an electro-magnetic field around Mazinger that disrupts the power feeding Mazinger and breaks down the Pilder's controls. He also warns that, should the electrical tension increase too much, Mazinger's mechanisms would melt.
In the episode in which Minerva-X appeared, Professor Yumi theorized that she was made of super-steel.
Mazinger is acronym for Multidimensional Automaton Zillion Infinity Neural Generative Exterminate Reverter
And in chapter 6:
Sayaka: Aphrodite A Immediate activation! number 1. Number 2. Number 3. Check! All Green! Retention bolt, begin release!
Telescoping Robot: Mazinger-Z has two extendable, razor-sharp cutters (properly named Iron Cutters) embedded into its forearms, several drilling missiles stuck into its upper arms, and its belly has a hatch to launch MORE missiles from. And then you have his Mid-Season UpgradeJet Pack, Scrander Jet, which can shoot shurikens. New Mazinger (an one-shot story set on an alternative universe) went deeper in this trope, and in one scene, many hatches opened up all over its body, revealing dozens of missiles underneath.
10-Minute Retirement: In episode seven several mobs had expressed their displeasure at Humongous Mecha stomping on their houses and them by harassing and assailing the heroes. Prof. Yumi had been hurt when a mob had thrown stones at him, Sayaka was so upset at her father hurt and protesters yelling at the gates of the Home Base she was thinking of quitting, and Kouji also decided just doing it after a big fight with her. Their retirement lasted until another Mechanical Beast attacked.
That's No Moon: A nearly literal example. Salude, Baron Ashura's submarine fortress was simultaneously a Cool Ship and an Island Base camouflaged itself like a real island (it had two parts: the lower part was a submarine Home Base and the upper part was an artificial island. Both parts were interconected via a tube. When Salude surfaced, only the upper part was visible). The first time Kouji saw it, he exclaimed: "That is not a island!"
Theory of Narrative Causality: Lampshaded sometimes. In one story Boss reassures his friends -Nuke and Mucha-, as facing a dire situation, telling that they will not die because they are the Plucky Comic Relief characters, and joke characters never die.
Dr.Hell: "Destroy me? How arrogant. A tiny island country intends to destroy Dr. Hell, the future ruler of the world? Alright! I swear I shall crush Japan in merely ten days! And the whole world shall witness the true power of Dr. Hell!"
This Is a Drill: Several robotical foes (such like Danchel and Stronger T4) were endowed with weaponized drills. As well, one of the weapons of Mazinger Z are drilling missiles located in its upper arms.
This Is Unforgivable: Whenever Kouji said this sentence you knew he was REAL angry, and someone was going to be summarily trashed in the near future. A good example was in the manga, after he learnt Dr. Hell had created a weapon was able to nullify gravity... and had used one whole city like subject test. Another two memorable instances happened in the Mazinkaiser movie (Mazinkaiser vs Great General of Darkness: at the beginning, after Lori and Loru's Heroic Sacrifice, and at the end, right before he absolutely destroys the Mykene empire army:
Kouji: Because you... Many people has died... THAT IS UNFORGIVABLE! 
This sentence was also used fairly often by Baron Ashura (to Kouji and his friends after being defeated) and Dr. Hell (to Ashura after his servant botched still another operation).
Those Two Guys: Nuke and Mucha, best friends and tag-alongs of Boss long before the start of the series. Before meeting and befriending Kouji they were two average, ordinary high-school students, but after meeting him their daily life includes battles between Humongous Mechas, fighting or fleeing from armies of Mooks, sneaking into enemy secret bases and basically surviving. Often they get -unwillingly- dragged -by Boss- in Kouji's adventures, and they provide with the rational counterpoint -and lampshading- to any stupid stunt Boss has come up with. Later in the series Boss got himself a Made Of Junk Humongous Mecha and required that they helped him to pilot it -much to their chagrin-. In Great Mazinger their situation did not get more normal, that with the monsters from Beneath the Earth invading the surface world bit and Boss demanding they help him to fight them like part of an absolutely helpless plan to woo Tsundere Jun Hono -Love Interest of The Hero Tetsuya, whom Boss can not stand-. In other series (Mazinkaiser, Shin Mazinger, Shin Mazinger Zero) of the Mazinger franchise they are given the same role.
And if you look to the three male leads of the trilogy, Duke (the older, more mature and more world-worn) is the prophet, Tetsuya (the most skilful and grimmest of them) is the lord and Kouji is the hunter.
Thou Shall Not Kill: Played with. Kouji gets forced to kill an IronMask in one of the first chapters of the original manga and he freaks out about it. Later he is wondering, worried, if he is a murderer now. A secondary character reminds him he just was defending himself.
Tokyo Is the Center of the Universe: Subverted. For start with, the Headquarters of the good guys are not in Tokyo but in the vicinity of Mount Fuji. Therefore, the enemy feels not compelled to exclusively target and attack Tokyo. A lot of Japanese cities are destroyed, ships are sunk in ocean, and often Mazinger-Z needed fighting in open sea (and in one chapter of one of the manga alternate continuities, it got deployed in another country). And in the Mazinger Z versus Great General of Darkness movie, the Mykene army struck New York, Paris, London and Moscow before striking Tokyo.
Tomato in the Mirror: Erika was an amnesiac girl that barely remembered her name. She felt an odd, devastating inner emptiness, but in spite of it she thought she was a normal girl. And then Baron Ashura appeared and revealed that in reality she was a human-looking robot built to murder Kouji Kabuto. She freaked out considerably -and understandably-, and she refused believing it.
Lorelei thought she was an average, little girl with a slightly eccentric and weird father. And then she found out that she was in reality a Robot Girl, and the key component to start a Humongous Mecha.
Tonight Someone Dies: Famously subverted in the episode titled Kouji Kabuto Dies In Lava!. Kouji did not die.
Too Dumb to Live: Several characters of the series (including the main characters) get at least one occasion where they seem determined to off themselves.
The civilians thought it was a good idea remaining near from the place where a Humongous Mecha and a Robeast were fighting, or blamed the heroes for the destruction and deaths Hell and his lackeys were responsible of, or pressed the Government to yield EVERY TIME Dr. Hell was blackmailing it are good examples.
A good, specific example is Yuri, Bratty Half-Pint Sayaka's cousin: Let's go over the facts, Yuri. You are a disabled, little Ill Girl can't run or move quickly because you need a wheelchair. You know there is a giant robot in the city, rolling over buildings AND people. Kouji has gone out to stop it after telling you very clearly you must stay in home because you are safer. Still do you insist on leaving the home and go to where the giant robots are fighting because you have a crush on Kouji and you want to see him? Okay, you can leave. After all, what can possibly go wrong?
Ugly Guy, Hot Wife: In episode 89 we meet an impersonator of Kouji and Shiro's mother. In episode 92 we meet Kouji and Shiro's supposedly late father. His wife was definitely beautiful. He... not so much. Although maybe he was more handsome when he was younger and he was not a cyborg.
Unbroken Vigil: Sayaka to Kouji in episode 52, as he was hospitalized after being badly wounded in a battle (she was also feeling guilty, since they had got a fight before -they bicker constantly, but this time it was serious- and she had refused backing in battle). And Kouji to his little brother Shiro in Mazinger-Z versus Great General of Darkness when he fell into coma after a ceiling crumbled onto him.
Uncanny Valley Girl: In Shin Mazinger Zero three beautiful, tall, ponytailed, blonde triplet girls called Gamia Q1, Q2 and Q3 transferred to Kouji's high school. Given that they were gorgeous and friendly, even if they behaved in a strange fashion and looked a tad weird, all boys in class started to quickly slobber at them. In reality they were three androids (appeared for first time in the Mazinger Z original manga and Mazinkaiser) sent to assassin Kouji Kabuto. Seemingly Kouji bought their masquerade, but shortly after he suggested them dropping their act, and he revealed that he had suspected it all along.
Underwear of Power: Both, Kouji and its robot wears (although in the Mazinger's case, it is metallic). Fem Bots -Aphrodite, Diana, Minerva- also wear it.
Unexplained Recovery: At the second-to-last episode, the Cool Airship where Dr. Hell was escaping got blown up. Whatever got left from him after that explosion surely sank in the ocean. Nonetheless he showed up again in the last season of Great Mazinger, his body grafted into a Humongous Mecha. One eyepatch covering his left eye was the only mark of the ordeal he had endured. Little explanation was given other than an statement of Big Bad and Physical God Emperor of Darkness had relived him and turned into one of his Warrior Monsters (and high commander of his army). It can may be worth mentioning many Mazinger-Z characters returned in the last episodes from the sequel, so maybe Executive Meddling was involved.
The Unfavorite: Kenzo Kabuto had two biological sons Kouji and Shiro and two adoptive children (Tetsuya and Jun). Although Tetsuya was clearly his favorite, he still showed he cared for his two blood sons. However, he got Jun completely neglected, treating her like a soldier, not making anything about her feelings of abandoment and her inner tensions, and he seldom shown he cared for her. It went so far that, before dying after his Heroic Sacrifice he pleaded Kouji that he treated Tetsuya like his brother and took care of Shiro... but he did not mention Jun at all. Nonetheless, his attitude drove Jun to think she could not be dependant on someone else and to develop a very strong-willed and self-reliant personality.
Unfinished, Untested, Used Anyway: During a battle Kouji decided using the Jet Scrander in spite of it had not been tested yet. To be fair, it was a "If I do not use it I'll die anyways" kind of situation, and he could not wait.
Ungrateful Bastard: People constantly blamed Mazinger and the Photon Intitute for the destruction the battles between the Mechanical Beasts and Mazinger cause, apparently forgetting if Mazinger Z didn't exist, all of them would be dead.
To be fair, a fight between Humongous Mecha can cause a great deal of collateral damage, no matter which side either participant was on as seen under Destructive Savior. Other continuities sometimes do show people getting killed in the crossfire, so some of their anger may be justified. Mind it doesn't excuse the fact that Kouji and his allies get crap for trying to help, just explain why.
Unobtainium: Japanium. It is a rare mineral can only be found on a lode on Mount Fuji and was discovered by Proffesor Kabuto. Mazinger Z, Aphrodite A and Great Mazinger are built with it and the Kikaiju after Dr. Hell stole a sample
Unresolved Sexual Tension: Kouji and Sayaka were the couple that definedBelligerent Sexual Tension. In spite of being attracted to each other, fierce competitiveness and pride issues on both sides prevented them from reaching an understanding and being together. It was not so bad in the original manga, though. And in another manga version, they kissed when they thought Kouji was going to die. He survived, but Kouji avoided Sayaka for a while because he was still too afraid and unsecure.
Unscientific Science: During the Final Battle in the Gosaku Ota manga chapters, Mazinger-Z was thrown in a Lava Pit... and it emerged unscathed. When Dr. Hell blurted out it was impossible (not even Made of Indestructium Mazinger-Z can endure a lava bath, let alone Made Of Flesh Kouji Kabuto), Kouji replied he had used the rockets located on Mazinger's feet to stir the lava and create an air bubble around his robot... which actually is harder to buy than the "It's Nigh Invulnerable and it emerged out very quickly" excuse.
Dr. Hell was infamous by fitting any sort of weapons on any place of the body of his Mechanical Beasts. Examples include Zaila (whose fingers fired missiles and whose horns were really drills), Brighton-J2 (those horns on its head? They are missiles), the ninja siblings Blazas S1 and S2 (missile launchers located on their shoulders and stomache), Solaris-S1 (its belt shoots a solar beam), Kajimofu-T7 (its palms shot beams and it had a missile launcher above its head), Gumbina-M5 (Combat Tentacles instead of eyes)...
Unwilling Roboticisation: All Co-Dragons -but Gorgon- and Mooks are Cyborgs created by Dr. Hell. He never gave someone choice in the matter or asked them if they want being turned into half-mechanical beings (and since Baron Ashura and his Mooks were corpses he revived by using cybernetic implants they could not refuse either). And in the case of Count Brocken, in one of the manga versions he states bitterly he was grateful to Hell because he saved his life... but he never wished serving him.
Use Your Head: Kouji -who is a full-blown Combat Pragmatist- has no qualms uisng that tactic when he is fighting with Mazinger-Z. It should be justified, since he is using his Humongous Mecha's head to ram the enemy instead of his own, but it is not, because Mazinger-Z's cockpit sits on the head of the giant robot.