Villain Team-Up: In the Mazinger-Z versus Devilman feature, Dr. Hell and the demons collaborate to take down Kouji Kabuto and Devilman. It may be subverted, since Hell used a mind-control device to enslave the demons, and he was mainly interested on taking down Mazinger-Z (he only sent some demons and Mechanical Beasts against Devilman because the demons warned him he would interfere).
Villainous Breakdown: It happened to Dr. Hell several times. The first of them happened in the THIRD episode, when he realized Juzo Kabuto still could surpass him and thwart his lifelong plans even after death. He destroyed all Mykene Humongous Mecha he had found, declaring them being uselesss, and he very nearly gave up right then. Another memorable one happened in episode 68, when finally he saw himself unable to triumph over Kouji Kabuto. He destroyed all of his newest Beasts, and swallowing his pride, asked help to Archduke Gorgon.
Villains Out Shopping: Several times, when the heroes infiltrated into one of the submarine fortress of Baron Ashura, he/she was taking a relaxing shower (and he/she did not appreciate being interrupted. Nobody -including the heroes, Ashura's minions and the audience- did, in fact). And often he/she was shown playing organ or drinking a glass of fine wine in his/her private chambers. Ashura could be quite laid-back when he/she wanted.
War Is Hell: From the opening narration from New Mazinger (an one-volume-long alternate manga version published in 1988): "A. D. 220X... Hostilities between north and south grow in fury as savage combat with new and ever more destructive weapons lays waste the once pastoral Earth. The remnants of mankind burrow deep beneath the surface. Their citadels, screened against the deadly bath of radiation, poke through the polluted soil like foul, mutant flowers. Their warriors, encased in giant combat armor against the air that once gave man life, live only to fight, and with luck, to fight again. Today, as every day, the flames of war rage in every corner of the globe. War without quarter. War without end. War for a race that has forgotten all other ways of life."
"Well Done, Son" Guy: One of the reasons Sayaka from could be so prideful, impulsive and hard-headed and was so obsessed with showing off was to get some measure of praise and acknowledgement from her Married to the Job, caring-but-emotionally-distant father. Unfortunately it did not work very well. For all times she risked her life, Gennosuke Yumi rarely gave praise.
Wham Episode: The final episode was an endless succession of shocking moments altered the status quo irremissibly: it was revealed that Gorgon was actually working for someone was infinitely more powerful and most dangerous than Dr. Hell, Mazinger-Z was utterly and easily defeated by a new enemy, a new and more powerful Mazinger showed up, named Great Mazinger and it was revealed Kouji's father was alive. The Wham factor was even bigger in the movie version of that episode, when the Mykene army razed to ruins New York, London, Paris and Moscow in one single stroke before leading towards Tokyo and destroying it as well, and at the end of the movie, the prophet removed his mask and revealed his real identity: Kenzo Kabuto, Kouji's father.
Kenzo: "He’s crying. My son is… My son…! Kouji Kabuto…!"
What Does This Button Do?: This series mixed this trope with with Falling into the Cockpit, and deconstructed both of them (funny and ironic, keeping in mind Mazinger Zwas the first mecha show where the pilot fell into the cockpit). When Kouji sat in the Hover Pilder (the flying device that controls Mazinger) for first time, he knew absolutely nothing about piloting. His little brother suggested that maybe it was a really bad idea, and he angrily replied he only needed to figure out what each button does. So when he began pressing random buttons to ascertain that... he nearly got himself and his brother killed. Mazinger-Z went on a rampage, destroying everything on its path, and it only stopped when Sayaka showed up and carefully explained to Kouji what he had to do (after getting baffled at the thought of someone doing something SO stupid). And it was way worse in the original manga version, since Kouji activated Mazinger-Z in the middle of a big city. To be fair, though, the person who had built Mazinger-Z was dead, so it was not like if Kouji could consult someone about it at the time.
What IS Evil?: In the manga version penned by Gosaku Ota, Baron Ashura kidnaps Kouji and suggests that he should join him/her. When Kouji states he has no interest in serving a criminal, Ashura gets indignant, and angrily utters that "good" and "evil" are nothing but concepts made up by humans, and the only true rules exhist in the world are the law of the jungle and the survival of the fittest.
What Measure Is a Mook?: The Iron Masks and the Iron Crosses are reanimated corpses turned into cyborgs, mindless and faithfully serve Dr. Hell and his henchmen. Kouji wonders in the manga if it is right kill them.
What Measure Is a Non-Human?: Discussed. In the original manga, three Iron Masks broke into Kouji's house. During the scuffle, he learns they are corpses turned into cyborg by Big Bad Dr. Hell and they are just Empty Shells programmed to obey. When one of them tries to convince him to die and become like them, Kouji angrily yells such a thing not even would be human. Still, Kouji has doubts about killing them, even if it is in self-defense, and when finally he gets forced to, he gets shell-shocked and later he wonders if he is a murderer now.
Usually Kouji and his friends think nothing of obliterating a Mechanical Beast in horrific ways (ramming a fist through its chest or punching its head or limbs out, dismembering it, blowing it up to bits, melting it, turning it into a heap of corroded scrap metal...), usually treating them like unliving, unfeeling machines. However, if a Beast exhibits more traces of independant thought, they may be more reluctant to fight and even can feel sorry about destroy it (such like Spartan K5 or Jenova M9).
Minerva-X is a complicated case. She was a Humongous Mecha that Dr. Kabuto designed. He programmed her to think independently, giving her the ability to act on her own and even feel emotions (including love). Everybody treated her like if she was alive and was a person, and mourned her death. And in Shin Mazinger Zero she has been traveling through time and dimensions, and we learn she is the original Minerva, so she MUST own an soul! Can it be said she is non-human, then? The implications are... unfortunate or mind-boggling.
Human-looking robots were treated like simple machines or human beings depending on the cirucmstance. The robots posed like Prof. Yumi or Kouji Kabuto were destroyed without a second thought. Robot Girls Erika or Lorelei were mourned when they died, and Shiro blamed Mazinger-Z for the latter's death and even temporarily hated him. However, the Gamia sisters were also Robot Girls and Kouji did not hesitate on destroying them (although he was very unsettled and even sickened after seeing their remains since they were REALLY human-looking). In Shin Mazinger Zero Shiro freaked out when he accidentally sliced one of them in half, thinking he had killed one girl, but his brother's friends told him she was only a robot to reassure him. The difference on treatment seems depending on how many human traits the robot exhibits rather what side it is on.
Great Mazinger: The Mykene are a civilization whose island was destroyed for an earthquake and were forced to seek shelter underground. To survive they grafted their brains into mechanical bodies. Therefore, the War Beasts are giant cyborgs once were humans, and they were more alive than any Dr. Hell's Mechanical Beast. However, Tetsuya and Jun never seem caring at all about destroying them. Then again, Tetsuya is a Blood Knight sees himself like a soldier fighting a war, and he accepts he can die at any time. So he treats the War Beasts how he expects being treated.
UFO Robo Grendizer: Duke did not particularly care about destroying Saucer Beasts... until a Vegan spy revealed to him that the Saucer Beasts he had been fighting are powered by the minds of his home planet's slain people (including his own little brother). Duke flipped out completely.
Before the outbreak of the war, Kouji was convinced Earth people could communicate with folks of other planets and become friends. After the Alien Invasion began, he did not seem feeling conflicted or remorseful about shooting faceless Mooks or Vegan ships. It was different if instead of an anonymous minion they had to confront an enemy they had got to meet and know about his/her personality or motivations, though. Then they could mourn him or her, regretting his/her death and wishing things could have been different.
Whip It Good: Several Mechanical Beasts used weaponized whips like weapons. Some examples are Gorias W3 and one of the Kikaiju from the Mazinger vs Devilman feature.
Wind is Green: When Mazinger-Z used Rust Hurricane it blew a powerful gale of wind from its mouth grill that disintegrated the enemy. At the first chapters that wind was green (although later it got changed to gray). It can be justified, since the wind was charged with corrosive particles could give him that color.
Wolverine Publicity: In the Super Robot Wars series, Kabuto Kouji is the worst offender/most notable example of this category (even more than Amuro Rei and the Getter Team). He appears in EVERY single Super Robot Wars games to date. Of course it makes sense due to the fact that Kouji is the FIRST mech pilot. Removing him would be like removing your ancestor out of the family tree.
And in most of Go Nagai series, Mazinger Z characters or mechas show up, even if it is only a brief cameo.
The Worf Effect: In the original manga, the eighteen-meters-tall Humongous MechaMade of Indestructium Aphrodite-A was sortied to stop a mysterious Humongous Mecha was rampaging through out a city and razing half of it. That mecha was Mazinger-Z, controlled by Kouji Kabuto who was learning the hard way that Falling into the Cockpit is not a good idea. When Aphrodite's fist failed in even denting the armor of the unknown robot, and she was easily tossed aside with a simple motion, Prof. Yumi knew that robot was extremely strong and dangerous.
Throughout the whole anime series, the Mechanical Beasts used Fem Bot Aphrodite-A or Diana-A to show how powerful they were.
And in an episode a secondary character called Saijyo showed he was a Badass by beating Boss (who in spite of being the Butt Monkey was a very competent and Acrofactic fighter).
And how they showed the Mykene War Monsters they were way more powerful and more dangerous than the Hell's Mechanical Beasts? They easily trashed Mazinger-Z.
Kouji himself was a victim of The Worf Effect throughout the whole UFO Robo Grendizer. Already in the first episode he got shot down easily by Vegan mini-ufos, forcing Duke to reveal his true identity to rescue him.
World War III: New Mazinger begins one hundred fifty years after World War Three between USA and Soviet Union at the start of twenty-first century. Nuclear weapons and nuclear winter wiped out ninety percent of humankind turned the planet into a radioactive, barren wasteland, and the survivors realigned in northern and sourthern superpowers and kept fighting. One century and half later, they are still fighting over whatever is left of Earth.
Worth Living For: In one episode, secondary character Erika asks Kouji why he goes so far to fight Dr. Hell, not matter how much he suffers or how many times he gets hurt. Kouji tells her it hurt a lot when his grandfather got murdered by Dr. Hell, and he does not want nobody else goes through that. And if Dr. Hell conquers the world, that is exactly what will happen to millions of people will lost their families and will be enslaved. It is because them he is fighting, not only for revenge.
Wrecked Weapon: Whenever Mazinger-Z fists -its most popular and most iconic weapon- were destroyed or shattered in one fight you knew Kouji was going to be in trouble. Maybe the first time happened when Kouji was fighting Spartan K5 and the Mechanical Beast easily ran its trident through its fist before beating the crap out of Mazinger-Z. A very memorable also happened in the Mazinger-Z versus Great General of Darkness, when General Juuma caught his flying fist before eating it.
Wrong Genre Savvy: Baron Ashura and Count Brocken hated each other. Dr. Hell thought it would be a good thing, since they would surely try to destroy Mazinger-Z harder to upstage each other. Or course, what happened was many operations and schemes went by the wayside because they constantly fought and got in the each other's way, and they were were unable to work together, ruining many joined missions, too. Hell's mistake was born of him believing he and his troops were a Five-Man Band instead of a Five-Bad Band.
Why Don't You Just Shoot Him?: In episode 39 Baron Ashura captured Kouji and Mazinger-Z and give him a "join-us-or-die" choice. After Kouji's predictable answer, Ashura sentenced him to death. Count Brocken was watching the scene through a monitor and he stated that Ashura beat around the bush too much, and he would just shoot Kouji.
Complexity Addiction: Later trying shooting him, Ashura started a bunch of power saws and drills to cut Mazinger-Z to pieces. To be fair, Kouji was inside Mazinger-Z, so one gun would do nothing, and they could not get him out.
Xanatos Gambit: Archduke Gorgon's master plan. He agreed to help Dr. Hell destroy Mazinger-Z with his visibly more powerful Mechanical Beasts. However his true intentions were to watch Hell closely and make sure both sides weakened each other battle after battle until one side won. Then, he would annihilate the weakened victor, and the Great General of Darkness -his real boss- would conquer the surface world without any real opposition. Consequently, he could not lose, no matter how the war between Dr. Hell and Kouji Kabuto ended. And, indeed, he was successful: he betrayed Dr. Hell at the worst possible moment for him, leaving him to die or personally murdering him -depending on the version-. Straight after, he sent several Mykene Warrior Monsters after Mazinger-Z, and they destroyed the Humongous Mecha. In one single day and from one single stroke he had looked after all his enemies. However, his plan failed due to a Spanner in the Works.
Year Inside, Hour Outside: In New Mazinger Major Kabuto was accidentally thrown in another dimension. He spend roughly one day in that place before returning to his own world. His partners told him he had been missing for one entire month.
You Have Failed Me: Amazingly averted with Dr. Hell, who admittedly, and understandably, can grow frustrated at the failings of his subordinates and punish them, but never kills anyone for trying their hardest and failing. Worst he did in the Mazinkaiser OVAs when Baron Ashura failed one too many times was throw him in a jail, and that was partly because Ashura had gone over his head. And even then, when he saw how determined Ashura was to make it up to him, Dr. Hell let him go anyways.
You Have Outlived Your Usefulness: In episode 31, three workers of the Photon Atomic Research Institute were kidnapped by Ashura and hypnotized in piloting the latest batch of Kikaiju Dr. Hell had built (Megaron P1, P2 and P3). However one of the weapons of Megaron generated such a heat blast would surely kill whoever was sitting in the cockpit. Hell and Ashura knew the three men surely would die during the battle, but as long as they died after they would have fulfilled their purpose, they did not care.
You Killed My Grandfather: It happens in the first episode, when Dr. Hell gets Dr. Kabuto assassinated, and Kouji vows to avenge him. And it again happened to Kouji and his own father, Kenzo, in the sequel.
An example taken from the original manga. Kouji has been cornered by several Mechanical Beasts, but Sayaka shows up with Aphrodite-A to give him time to reach Mazinger-Z: 
Episode 6: A Mechanical Beast is trashing one city to keep Mazinger-Z and Aphrodite-A busy as a second Beast and a squad of Iron Masks take over the Photon Atomic Research Institute. Kouji tells he will deal with the first Beast to let Sayaka go to protect the Institute.
Another example taken from episode 74: A Mechanical Beast was completely trashing Mazinger-Z around. Sayaka -as piloting Aphrodite-A- stepped between both and stood in the way of the Beast to protect Kouji, receiving all its attacks to prevent it from killing Kouji and destroying Mazinger-Z even though it meant Aphrodite-A was destroyed for good.
Episode 92: Kouji is hurt and can not fight, so Boss knocks him out, and he and Sayaka deploy their Humongous Mecha to try to hold back the Mykene Warrior Beasts marching towards the Institute. They fail badly.
Chapter 6 from Shin Mazinger Zero: Three assassins Robot Girls -Gamia Q1, Q2 and Q3- are attempting to get Kouji murdered, but Sayaka and Boss to step in the way to protect him: 
You Watch Too Much X: In the first chapter of the manga, Mazinger ends up going on a destructive rampage during Kouji's first attempt to pilot it. When some concerned citizens try to tell the police about it, their claims of a "giant monster" destroying the city are dismissed with "You watch too much TV."
Your Size May Vary: The applied scale was not consistent at all, and it could vary from one chapter to another or even in different scenes of the same chapter. Sometimes the Humongous Mecha were too big or too tiny, and the human beings and other objects too tiny.
Zeerust: This trope was abundant in the series, evident in many of the vehicles and SuperRobots in the series. A case that stands out is an episode in which Baron Ashura captures and analyzes Aphrodite A, only for the disc with the data to be destroyed. It's a good thing the villains didn't have e-mail.
Ironically, in another episode Ashura stored data in a sort of card had to be inserted into a computer to display the information stored in it.
Zerg Rush: Baron Ashura often sent large numbers or Iron Masks to attempt to murder Kouji Kabuto -and his friends- when he was out of Mazinger-Z or to try to overwhelm or get Mazinger-Z and Aphrodite-A confused (and it worked with Aphrodite once. They were so many, so fast and so annoying they got her distracted and slowed her down). Curiously, it was inverted in the original manga once: in one of the first chapters three Iron Masks crawled in Kouji and Shiro's home and they almost got Kouji killed.
In the original manga Dr. Hell also used that tactic in the Final Battle, mobilizing two of his armies, a Cool Ship, a Cool Airship and forty Mechanical Beasts against Japan and the Mazinger army. In Mazinkaiser Dr. Hell also used twice that tactic (and it worked in one of them!) and The Mykene Empire sent huge numbers of Warbeasts all over the world to conquer the surface. Similarly, the Vegans from UFO Robo Grendizer attacked Earth cities with vast fleets of mini-ufos, often backed by at least one mothership and several Saucer Beasts.
Zettai Ryouiki: Sayaka Yumi tended to wear short skirts whether she was wearing her school uniform or casual clothes. And later in the series she wore a very short white-red skirt and knee-length, white boots. In the manga versions more female characters wore attires or uniforms that showed their tights, such like the Gamia or Minerva-X in Shin Mazinger Zero.