The leader of the Nexo Knights. Righteous and dutiful, he's dedicated to being the best knight he can be. When not in battle, he tends to train to improve his skills even further.
- Animal Motif: Birds, or specifically, a falcon. It's his family crest, he uses flying vehicles including a jet called the "Falcon Fighter", and he also uses jetpacks.
- Back from the Dead: In episode 2 of Season 4, he's resurrected by Monstrox and turns evil, then turns good, then forces Macy to petrify him again after he becomes too dangerous, then he's resurrected again by the magic inside him.
- BFS: His weapon is an incredible huge sword.
- Busman's Holiday: When forcibly sent on vacation by everyone else, the resort Clay's at just happens to be where the Book of Cruelty has wound up.
- The Comically Serious: The steadfast, strict, and dutiful Clay is often put into comical situations due to his teammates' more colorful personalities.
- Farm Boy: In the first episode, he's noted to come from a farm.
- The Leader: Obviously, since he's also the protagonist.
- Of Corpse He Is Alive: What the other knights put his petrified body through in the first episode of Season 4.
- Punny Name: His name is a pun on his signature weapon, a claymore. It also overlaps with Meaningful Name when you see that in "Knights of the Realm: Part 1", he was given a claymore as a child when he was defending a fellow knight from his cheating sparring partner.
- Taken for Granite: His fate in Season 3. He gets better.
- Why Did It Have to Be Snakes?: He's afraid of failure.
- The Worsening Curse Mark: Suffers this in the third season as his body is slowly being turned into stone. By the end of episode 9, he's turned to stone completely.
- Worthy Opponent: Magmar saw him as this, but it's only revealed in Season 3.
The son of a wealthy family, Lance has a tendency to put his needs and wants before his knight's duty due to his upbringing. He doesn't particularly like training or being told what to do, which usually puts him at odds with Clay.
- Animal Motif: Horses. At least thrice he's had vehicles that look like or are horses.
- Attention Whore: He loves the spotlight. Conversely, he strongly dislikes it when people aren't paying attention to him.
- Drama Queen: Wails dramatically about how his day is ruined because his phone crashes.
- Foil: To Macy. Both of them were born into a higher-class family than the rest of the team, and both had Fantasy Forbidding Parents trying to enforce the family's traditions on them instead of choosing a job they liked, the difference being that Macy got what she wanted by becoming a knight, while Lance wanted to be a celebrity instead. Also, while Macy wants to be treated like an equal despite being a royal, Lance, who is only a nobleman, is an Attention Whore and hates doing anything himself.
- Headbutting Heroes: With Clay, at first. The two spend all their time bickering about what to do, with Lance disregarding Clay just 'cuz.
- Humiliation Conga: After being an arrogant prat while filming the Golden Castle remake, Lance's armor malfunctions during Jestro's attack, which is all filmed by the director and shown to the entire kingdom at the film's premiere, making everyone laugh at Lance, and causing his agent to dump him in an instant.
- Idiot Hero: He has no idea how to operate his phone, thinking when Ava talks about "back-up" that he needs to literally take a step back.
- It's All About Me: Has the habit of trying to direct all the attention to himself, boasting about his good looks and talents.
- Jerk with a Heart of Gold: As arrogant and condescending as he can be, Lance is steadfastly dedicated to protecting the kingdom.
- Jet Pack: Gains one with his ultra armor form. It doesn't always work.
- Lazy Bum: At first. He even mentions his idea of training is going out clubbing all night.
- Pretty Boy: His looks have earned him lots of adoring fans.
- Punny Name: His name is a pun on his signature weapon, a lance.
- Skewed Priorities:
- When the rest of the team comes down with a serious case of flu, Lance is the only one unafflicted, but is more concerned with whining about his hair.
- When the queen has been kidnapped by Ruina, Lance spends most of the chase bickering with Axl about a game they'd been playing earlier.
- Small Name, Big Ego: When given the part of a lead in a movie, he insists the movie be rewritten to be even more about him than it already was, and starts throwing a tantrum when Clay and Macy dislike the results.
- Spoiled Brat: Big time. Whipperella even states that Lance is a "Spoiled party boy", though he's also willing to protect the kingdom of Knighton, and is a good person most of the time.
- Upper-Class Twit: So very much. A frequent complaint of his is that he won't do something because he has people to do it for him.
- Why Did It Have to Be Snakes?: He's afraid of obscurity.
The thrill seeker who's unable to stay still, Aaron is always ready to participate in anything exciting and dangerous.
- Animal Motif: Foxes. His family crest is a fox, and it's his last name.
- Archer Archetype: He wields a crossbow in battle.
- Expy: He seems to be heavily based on Lewa from BIONICLE, as a green-armoured thrill seeker, though his Weapon of Choice comes from Kongu.
- Full-Frontal Assault: In both "Fright Knight" and "A Little Rusty", Aaron is completely stripped of his armor, leaving him naked in front of everyone to see.
- Good Scars, Evil Scars: Has a notable scar over his right eyebrow.
- Malicious Misnaming: Uses it against Whipperella, which causes her to have a breakdown.
- Mellow Fellow: Is this for the most part.
- Naked People Are Funny: Aaron doesn't mind being losing his armor and walking around naked, and even states that he likes to "Rock the Commando Look" in "Fright Knight" and "A Little Rusty".
- Nothing Is Scarier: His literal fear is doing nothing.
- Punny Name: His name is a pun on arrow.
- Take Up My Sword: Becomes Clay's successor when he turned completely to stone.
- Totally Radical: The poster boy for this trope in the series.
- Why Did It Have to Be Snakes?: Initially Averted when it seems as if absolutely nothing can scare him, but it turns out that for him, Nothing Is Scarier.
The Knights' only female member, Macy is the daughter of King and Queen Halbert. She much prefers fighting monsters to her duties as a princess.
- Animal Motif: Dragons. It's her family crest on her mother's side, she has a robotic dragon in Season 3, and a jetpack in Year 3.
- Dragon Rider: In Season 3, she gets a robotic dragon, which is designed to bond with her as she uses it.
- Expy: She's clearly based on Princess Storm from the 2000 Knights Kingdom 1 theme. With the whole being a princess who wants to be a knight and a father who doesn't really agree or approve of her choices. Heck she's even got red hair like Storm.
- Fanboy: Of the Ned Knightly stories, especially the Golden Castle. She hates what Lance's ego-trip does to the attempted remake.
- In the Blood: Her mother, the Queen, has a fondness for smashing things with maces as well.
- Kicking Ass in All Her Finery: Despite her hatred of her impractical dress, during Season 3 she manages to get into a fight while wearing one.
- Punny Name: Her name is a pun on her signature weapon, a mace.
- Red Is Heroic: Macy's armor is red.
- Talking the Monster to Death: What she technically did to Lavaria.
- Tomboy Princess:
- Why Did It Have to Be Snakes?: Her worst fear is being a princess, forced to go around in an impractical fancy dress.
- Youthful Freckles: She's got freckles on her face in the television series.
- An Axe to Grind: He wields various axes.
- Animal Motif: Bulls. His armour just happens to look an awful lot like one, and he has one as his family crest.
- Berserk Button: He takes his cooking seriously.
- Big Eater: He is as passionate about eating as he is about fighting.
- The Big Guy: The strongman of Nexo Knights. In the sets, it's represented by his having a larger minifigure than the others.
- Genius Bruiser: Despite his brutish, simple-minded appearance, he can be quite clever when he needs to be, as seen in "The Maze of Amazement", where he was able to figure which of the maze's walls were fake by strumming his lute and listening for echoes.
- Non-Standard Character Design: He is a Top-Heavy Guy, with far more detailed hands than the other characters.
- Only One Name: While he has a known family, they don't have a surname.
- O.O.C. Is Serious Business: As he even notes, when ill he isn't even hungry, and becomes convinced this means he's dying.
- Punny Name: His name is a pun on his signature weapon, an axe.
- Why Did It Have to Be Snakes?: He's afraid of there being no food to eat.
- Animal Motifs: Chickens (or roosters). His insignia is a chicken, and he has been known to use the Rooster's Cry Nexo Power.''
- Badass Adorable: Despite looking like he couldn't hurt a fly, the guy can put up a fight with his gadgets.
- Badass Biker: His Year 3 vehicle is a motorbike.
- Black Knight: His Powered Armor made him this with its black armor.
- Bling of War: His Year 3 sets give him the same golden armor as the main knights.
- Catchphrase: "None shall pass!"
- Child Prodigy
- Cloud Cuckoolander: Is this compared to Ava.
- Composite Character: As stated below, he has characteristics of two Monty Python and the Holy Grail characters: Sir Robin and the Black Knight.
- Dark Is Not Evil: His Black Knight persona is dark and menacing in appearance, but he uses it to help people and bring fear to the villains.
- Drop the Hammer: His Year 3 sets make hammers his weapon.
- Gadgeteer Genius: He serves as the team's tech department, all on his own.
- Mundane Utility: The Rooster's Cry power just makes the sound of a rooster cawing. Robin uses it to wake up the knights when they're passing out from exhaustion.
- Nice Guy: He's never rude to anyone and always ready to help the knights or squirebots out.
- The Pirates Who Don't Do Anything: Despite still studying at the Knights Academy, he is hardly ever seen there, although his Year 2 description from the official web site does mention him being on a year of "independent study".
- Powered Armor: Used one for awhile.
- Shout-Out: To Monty Python and the Holy Grail. However he's MUCH more braver than his namesake, though he still sports the chicken symbol. There's also the fact that his mech suit is called the Black Knight (And also suffers the same fate as its namesake).
- Teens Are Short: In the show, he's pretty young, and this is represented by using the shorter leg pieces in his toys, though his Year 3 uses the regular leg pieces, suggesting he's gotten a growth spurt.
- Ambiguously Jewish: A snarky Brainy Brunette who often argues with Merlok and the only hero shown demanding payment for her services (even if only once), but with no word on her religion (unsurprisingly for a LEGO-based cartoon) and no way to see if she observes kosher or Sabbath.
- Child Prodigy
- Deadpan Snarker: Oh so much.
- Gadgeteer Genius: Not as much as Robin, but it's her computer skill that allowed her to unlock Merlok 2.O and send the knights their Nexo scans.
- Not so Above It All: Even Ava can't stand Clay's relentless training regime, and joins with the others in shipping him off for a vacation, so she can slack off.
- The Pirates Who Don't Do Anything: Despite her promotion to a junior knight as of Season 1 finale, she is the only member of the team (if you include her and Robin) who never fights monsters and doesn't seem to have any combat skills. In general, her only job seems to be scanning Nexo Powers for her comrades to use.
- Punny Name: Ava Prentis is one for apprentice.
- Tsundere: As much as Ava comes across as a grump, she does care about Merlok, yelling she doesn't want to lose him during the Season 2 finale.
- Colour Motif: His hologram form is associated with orange.
- Heroic Sacrifice: Sacrifices himself to take out Monstrox for good.
- Last of His Kind: Merlok is the only wizard left in Knighton. And then he goes boom trying to stop Jestro taking the Book of Monsters.
- Mentor Occupational Hazard: Technically, he's already fallen victim to it. It just didn't keep him down.
- Nice Job Breaking It, Hero: Sacrificing himself not only didn't stop Jestro and the Book, but it also scattered the various evil books around the kingdom.
- Poor Communication Kills: Partly on account of senility. At the beginning of Season 2, he tells the knights they need to look for something in the library, but can't remember what. It's only after Jestro and the Book have found it, got it and fled that he remembers what it is.
- Wizard Classic: How he looked in life.
- Bling of War: He's got fancy golden armour.
- Cowardly Lion: He's not much of a fighter. In fact, he's pretty afraid of pain. And anything scary in general.
- Epic Fail: After Jestro takes out all the power in the city, he tries reassuring everyone, and does such a bad job he sends them into a panic.
- Fantasy-Forbidding Parent: He tries to do everything he can to talk Macy out of doing anything dangerous, including not giving her a shield at her graduation ceremony.
- The Good King: They don't call him "King Halbert the Benevolent" for nothing.
- Kick the Dog: Wanting to protect his daughter is all well and good, but his actions at the graduation ceremony are seriously humiliating for her.
- Overprotective Dad: He greatly dislikes the idea of Macy risking her life as a knight, and would rather she simply stay in the castle, where he can keep an eye on her, although over the course of the series he gradually becomes more acceptive of Macy's choice.
- Powered Armor: Eventually acquires one for himself, and wears it throughout Season 3 to always be ready for a battle.
- Badass in Distress:
- In her toy forms, in both sets she's been released with, Queen Halbert has or is being imprisoned by the bad guys (and given both times her minifigure comes with a furious expression,she's not taking it lying down).
- She gets abducted by Ruina during Season 3.
- Berserk Button: Anything trying to harm her husband and/or daughter.
- Bling of War: Matching her husband's.
- Drop the Hammer: Wields a war-hammer in fights.
- Grievous Harm with a Body: During Jestro's first attack on the city, she fought off some monsters by using one of the guard robots as a club.
- Open-Minded Parent: Unlike her husband, the queen is fine about Macy being a knight.
- Royals Who Actually Do Something: Unlike her husband, the queen is a fighter.
A royal jester with self-esteem issues, Jestro's attempts at entertaining people usually fail miserably, resulting in him becoming the laughingstock of the kingdom.
The Book of Monsters manipulated him to become a villain, and he embraced his new role in hopes of finally being good at something.
- Bad "Bad Acting": He's never been good at acting, even as a child.
- Berserk Button: Being laughed at makes him lose his temper.
- Brainwashed and Crazy: Throughout Seasons 3 and 4.
- Character Tics: "The Knights of the Realm Part 2" revealed that he juggled as a kid whenever he was nervous.
- Cloudcuckoolander: He insists the earth is donut shaped.
- Evil Costume Switch:
- His jester's outfit turns to red-and-blue when he touches the Book of Evil.
- Inverted when he turns good, donning a blue-and-orange outfit with armor on it.
- Evil Feels Good: Enjoys being evil because it's something he's moderately good at.
- Evil Makes You Ugly: He looked like an ordinary person before he touched the Book of Evil. The initial effects include his teeth and eyes turning yellow. As time goes by, Jestro starts looking less and less human at all. Case in point, by the Season 3 premiere, his skin now looks like electricity is coursing through it.
- General Failure: His first act on summoning General Magmar, who the Book assures him is a military genius? Put the man to work rigging up booby traps, rather than coming up with a winning strategy.
- Harmless Villain: At first, despite wanting to be evil, Jestro is utterly terrible at it.
- HeelFace Revolving Door: He started out good, but was manipulated by the Book of Monsters into working with him. He reformed in Season 2, but was once again corrupted in Season 3. After Season 4, he manages to side with the Knights.
- Horns of Villainy: Whenever he does something truly evil, his jester hat twist itself to look like a pair of horns. This continues in Season 3 where the hat actually emits a torrent of electricity between the two points.
- Horrible Judge of Character: The Book of Monsters easily manipulated him to do his bidding. Jestro later admits that he's never been good at reading people.
- Red Eyes, Take Warning: Well more of a red pupils during Season 1 and 2.
- Supernatural Gold Eyes: His eyes glow gold whenever he starts putting effort into being evil.
- Took a Level in Badass: Along with a level in Jerkass, during Season 3. He becomes more evil, and more of an actual threat, even talking back to the Cloud on occasion.
- Walking Disaster Area: His attempt at doing a magic show ends with him flinging a power mace into the nearest wiring, cutting off power to the entire city. He also makes a comment in episode 3 that he badly smashed up Ye Olde Royal RV when he performed a show in it.
- Yank the Dog's Chain: Just as Jestro finally gets a chance to be a good comedian, the Book betrays him and preps him for a case of Demonic Possession.
- And again in Season 3, where he finally finds a job as a weather reporter and tries to make peace with Knightonians only for Monstrox to brainwash the guy into servitude.
Book of Monsters/Monstrox
A sentient evil spellbook and Jestro's mentor. The Book of Monsters is highly manipulative, requiring an unsuspecting pawn to summon monsters from his pages due to his lack of limbs. He seeks to consume all the eleven books of black magic, which enhance the powers of the monsters summoned through him.
In reality he is Monstrox, the arch necromancer. A century ago Merlok turned him into a book and his evil powers were separated into the eleven spellbooks he seeks.
- Card-Carrying Villain: In The Book of Monstrox he constantly adjusts his speech to insert as many evil metaphors as possible. He also outright claims that dark magic is more interesting that magic to help mankind.
- The Corrupter: Is responsible for Jestro becoming evil not once, but twice! In his cloud form, he can do this simply by zapping something with a bolt of lightning.
- Deadpan Snarker: Often, especially towards Jestro.
- Elemental Powers: As a cloud he can use lightning attacks, and even then it's hinted at with the monsters he created (Lava monsters when he was still a book, followed by turning statues into stone monsters).
- Evil Smells Bad: According to Jestro, he stinks. The Book retorts that he's been sitting on a shelf for a hundred years.
- Fallen Hero: Monstrox used to be one of the Wizard's Council, until the magic he was researching started corrupting him.
- Killed Off for Real: The non-televised ending has Clay utterly destroy him for good.
- Laughably Evil: He is generally one of the funniest characters in the show, but his monologuing in The Book of Monstrox deserves a special mention.
- Not Quite Dead: First, the Knights destroy his book form, turning him into a cloud. At the end of Season 4, he loses the cloud form, but comes back as Monstrox 2.0.
- Omnicidal Maniac: In Season 3, his plans escalate from conquering the kingdom to outright destroying it.
- Red Eyes, Take Warning: His eyes go red with his power up at the end of Season 3.
- Sealed Evil in a Can: Technically he is this, way more in Season 1 and 2 if you consider his lava monsters trapped inside his pages.
- The Man Behind the Man: Back when he was still the Book of Monsters, he pretended to be a mentor of sorts to Jestro, when in truth he used him to become Monstrox once more.
- Tome of Eldritch Lore: He was a spellbook filled with nasty spells and summonable monsters.
- Villainous BSoD: Finding the Lava Monsters going pacifist sends him into a funk, until it turns out they tricked Jestro.
- Voice of the Legion: During Season 3's finale, thanks to the Forbidden Power boost.
Roberto Arnoldi is a sculptor who used to work for King Halbert. One day, he was commissioned to make a "smashing" statue of Queen Halbert. When he literally made a picture of Queen Halbert hammering some Scurriers, King Halbert was displeased, and fired him, despite the Queen actually liking it. Upon meeting Jestro and the Cloud of Monstrox, Roberto sided with them in order to get revenge on Knightonia, starting by making monster for Jestro and Monstrox.
- Cloudcuckoolander: Even without his literal-mindedness, Roberto's brain is often somewhere else. When Jestro mentions needing "wheels", Arnoldi starts talking about doing something with wheels of cheese.
- Les Collaborateurs: Unlike Jestro, he joined Monstrox willingly to get back at the king for humiliating him.
- Literal-Minded: Takes what people says literally, for example, when Jestro asks for a rolling headquarters, he literally made a moving base with a noticeable head up front. When asked to make a "smashing" statue of the queen, he made it one of her smashing things.
- Mad Artist: Considering he's aiding Jestro and Monstrox in overthrowing Knightonia, he qualifies. In fact, Season 3 finale has him happily carve the image of the Stone Colossus ravaging the kingdom, showing he doesn't give a crap about what happens to it.
- Mook Maker: Has taken this job, as well as creating the new mode of transportation for the bad guys.
- Toyless Toyline Character: He's not present in the toyline.
A group of fire-based creatures who serve Jestro.
- Does Not Like Shoes: Some of the Magma Monsters go barefoot, including Lavaria, Beast Master and Crust Smasher. In the Character Encyclopedia, Lavaria's entry notes that she has "bare, clawed feet for silent sneaking".
- Good Colors, Evil Colors: They favor red, orange, yellow and black.
- HeelRace Turn: They seem to have become good after the events of Season 2 and just want to live in peace.
- Mooks: The Ash Attackers, Crush Smashers and Flame Thrower monsters.
- No Body Left Behind: Whenever they're hit with Nexo Power, though that's not much of a problem though as they just return to the Book of Monsters and can be summoned again.
- The Swarm: Seems to be a preferred tactic of magma monsters.
- The Dragon: Used to be Monstrox's right-hand monster. And still is, in fact.
- General Failure: He is apparently the strongest monster the Book ever produced, and is also incredibly clever. That doesn't mean he wins fights very often.
- Samurai Ponytail: Seems to be sporting one.
- Walking Shirtless Scene: His torso is always exposed.
- Wicked Cultured: Speaks with a refined British accent.
- The Beastmaster: Able to tame any monster, even the ones conjured up through the Book of Chaos.
- Epic Flail: Wields two of the minion magma monsters as this.
- Eyepatch of Power
- Gadgeteer Genius: He's the one who built the Jestromobile. However, he's not very good at it, since Jestro complains soon afterward. The Book of Monsters explains it's because of the influence of the Book of Chaos - Jestro told him what to do, he just didn't explain very well.
Flama and Moltor
- Bash Brothers
- Fog Feet: Flama has no feet. It's represented in toy form by a version of this.
- Power Fist: Moltor's hands are oversized, presumably to aid with punching folks.
A very talented spymaster, Lavaria is a lava monster who specializes in espionage and thievery. She fulfills her missions without making a single sound.
- Bare Your Midriff: Her top exposes her toned midriff.
- Bat Out of Hell: Her Ultimate form has bat-like wings.
- Femme Fatale: Her introduction is about as close as she can get to being one without destroying the metaphorical radar, even coming complete with Sexophone.
- Ignored Enamoured Underling: She pines for Jestro, but he doesn't return the affection. At least, so the show's website says.
- Master of Disguise: Manages to disguise herself as a robot, with no-one being any the wiser.
- Paper-Thin Disguise: She infiltrates a cooking competition simply by putting on a false mustache. That's it.
- Stealth Expert: One of her skills is sneaking around silently to gather intelligence on the Knights and their allies.
- Yellow Eyes of Sneakiness: Fitting, for a spymaster.
Burnzie & Sparkks
- Cyclops: Sparkks.
- Dumb Muscle: Burnsie is incredibly strong, but very stupid. He's still smarter than Sparkks.
- Starter Villain: The brothers are the first non-Mook monsters Jestro learns to summon, and the first the Knights face.
- Those Two Guys
- Volcanic Veins
- Berserk Button: Aaron appears to be this for her.
- I Know What You Fear: Try to use this against her enemies, but it doesn't work if she can't figure out which thing they're afraid of.
- Reality Warper: Her whips cause their target's worst fears to appear out of nowhere, rather than just making them think they're seeing them.
- Reptiles Are Abhorrent: Unlike fellow female monster Lavaria, Whiperella is much more reptilian in appearance, and not considered as attractive by the story.
- Snake People: The lower half of her body is a snake's tail.
- Whip It Good: Her weapon of choice, as the name suggest.
The villains in the second year. After his defeat in the first year, Monstrox was transformed into a cloud with the ability to infuse stones with evil energy by zapping them with lightning. He made use of this ability to not only animate ordinary rocks and statues, but old minions of his Taken for Granite during his battle with Merlok and creations made by Roberto Arnoldi.
- Back from the Dead: Unless hit with the Combo-Nexo power, their bodies will just turn back into stone, which Monstrox can quickly fix with his lighting strikes.
- Dumb Muscle: The rank-n-file are good for rushing the enemy, but... well, they've literally got rocks for brains. Even instructions as simple as "stay here" confuse them.
- Evil Counterpart: Some of them have access to the Forbidden Powers, evil versions of the knights' own Nexo Powers.
- Good Colors, Evil Colors: They favor pale blue, gray, purple and a little black.
- Hired Guns: Most were monsters created by Monstrox, but there are some whose origins aren't connected with the archnecromancer.
- Karma Houdini: Season 4 finale has them simply escape the battlefield after Monstrox's defeat and remain active, with the only exception being the Roguls who get petrified.
- Terrible Trio: Most of the high ranking Stone Monsters are usually found in a set of three.
- Theme Naming: Most of their names begin with "r".
One of the leaders of the Stone Monster army, a general who once battled alongside Monstrox.
- Combat Pragmatist: According to The Book of Monstrox, he likes employing these tactics.
- Cool Sword: A double-bladed lightning sword.
- Hell Is That Noise: His signature trait is the excessive grinding he makes with his teeth.
- I Surrender, Suckers: His "Wacky Wingover" flying move, where he pretend to flee from the fight, then pounce when he's pursued.
- Taken for Granite: First he got set on fire, and then he got taken for granite.
- Uniformity Exception: Garg looks like all the other gargoyles, except he's black where they are grey. Apparently this was due to Monstrox hitting him with fireballs during a battle with Merlok by accident.
- The Corruptible: Due to guarding the forbidden power, each individual Rogul has the ability of the forbidden power they were guarding.
- Fog Feet: With hovering rocks circling them.
- The Voiceless: They can't speak.
A trio of flying Stone Monsters that are good at grabbing.
- Aerith and Bob: Their names are Hilda, Ingrid and Bullwicker.
- Harping on About Harpies
- Taken for Granite: The trio were turned to stone while attempting to nab the Forbidden Power of Ravaging Rot.
As the name suggests they are three evil golem brothers (Roog, Reek and Rumble) who once battled the wizard council in the past. They now serve Monstrox and Jestro in their attempt to rule the kingdom.
- Came Back Wrong: Rumble's body was ruined when he was chiselled out, resulting in his current status as a car.
- Car Fu: Rumble does this, literally, as his body is now a transport for his two brothers.
- Violent Glaswegian
- Enigmatic Minion: Her strange actions seem to hint at her having a goal different from Monstrox's, although what it is will never be known due to the show's cancellation.
- Fallen Hero: She was a member of the Wizards' Council before Monstrox somehow corrupted her.
- Karma Houdini: At the end of Season 4, she's still out there. And then the show ended.
- Luke, I Am Your Father: She's Clay's mother, and Merlok's sister.
- Sinister Scythe: A lightning scythe.
- Taken for Granite: Merlok turned her into a statue, hoping to restore her to her good self.
The greatest of Monstrox's generals, who led an entire army that was turned to stone alongside him by Merlok.
- Cool Sword: A lightning blade with a skull on the hilt.
- Even Evil Has Loved Ones: He cares for his Krakenbeast, "Dolly".
- Intelligible Unintelligible: He speaks a strange language that only Monstrox can understand.
- Names to Run Away From Really Fast: Lord Krakenskull.
- Taken for Granite: Turned into stone by Merlok before the series.
The villains of the final year, created by Monstrox 2.0.
- Abnormal Ammo: Their weapons shoot spider-like critters, which can infect objects and people with Monstrox's tech infection.
- The Corruption: They can corrupt robots to join their side. Such as Lance's servant, Dennis.
- Evil Counterpart: They're the closest to the Nexo Knights out of all the villains, with their own Mecha-Mooks from corrupted Squirebots, mechanical vehicles, and Monstrox 2.0 even granting them their own Nexo Powers to use.
- Good Colors, Evil Colors: They prefer black, green and grey.
- Our Vampires Are Different: They're styled after vampires, with pale skin, dark clothing, red eyes and prominent fangs, but instead of feeding on blood and being associated with bats, they're associated with spiders via their critters and spread a technological virus.
- Punny Name: Several of the Mooks have "Byter" in the name, and they're effectively technological vampires.
- Sickly Green Glow: Their primary color, befitting of a force who literally infect machines and people.
- Anime Hair: Unlike most of the Tech Monsters, Pola has a large head of purple hair.
- Badass Biker: She and Fred ride the combining Twinfector.
- Smurfette Principle: Pola appears to be the only female Tech Monster.
- Tag Team Twins: With Pola, riding the Twinfector.
- Aerith and Bob: A Tech Monster named...Fred.
- Anime Hair: A limited edition minifigure revealed that Fred has the same purple hair as Pola, though he usually wears a helmet.
- Badass Biker: Rides the combining Twinfector with Pola.
- Cool Sword: Wields one in his limited edition minifigure.
- Tag Team Twins: With Pola, riding the Twinfector.
- Evil Counterpart: He's juxtaposed against Lance, fighting alongside Lance's former Squirebot, wielding a spear and appearing somewhat similar to the vehicle Lance uses against him, the Hover Jouster.
- Mecha-Mooks: Notably, he's shown to have a personal CyberByter, the infected Dennis.
- Nonstandard Character Design: Has a mechanical lower torso with four legs that appear to have blasters mounted on the end.
- Spiders Are Scary: His lower legs are four mechanical ones.
- The Berserker: He wears less armour than his fellow Tech Monsters, appears constantly enraged, and pilots the heavily armed Berserker Bomber.
MegaByter, MechaByter, and VanByter
- Mooks: They serve as the more basic soldiers of the Tech Monsters.
- You Are Number 6: VanByters have numerical designations; VanByter No. 407 and 307 are seen in the sets.
Infected Squirebots that serve as the Tech Monsters' Mecha-Mooks, including Lance's trusted squirebot Dennis.