Ryan WalkerMECH-X4's technopath pilot, (ir)responsible hero.
- Happily Adopted: By the Walker family.
- Mommy and Daddy Had a Good Reason for Abandoning You: According to Leo, the reason Ryan's parents put him up for adoption was because someone-implied to be Harper-was after them, and they wanted him to live a normal life.
- Synchronization: Ryan is bonded to MECH-X4 once he attaches himself, so whatever damage is done to the robot also hurts him. However, repairs to the robot can also heal him without the need for medical facilities.
- Technopath: Ryan is one of these, using it to control MECH-X4. He also uses it to interfere with technology, usually to get him and the crew into places or to help them escape. It's revealed in Let's Survive in the Woods! that there's a limit to it: Ryan can't affect technology that isn't already turned on. He eventually becomes powerful enough to control the robot remotely in short bursts.
- Thou Shalt Not Kill: Throughout Let's Get The Big Bad!, Ryan outright refuses kill any human being, no matter how bad they are. He even attempts to save Principal Grey even though she callously betrayed them. In Let's Destroy Some Ooze!, Killing in Self-Defense is not an option; he stops Spyder from attacking the military who were misled into thinking that MECH-X4 was a threat due to Seth Harper because they were "just doing their jobs".
Mechanic of MECH-X4, Ryan's brother, star athlete of Bay City High, awesome (according to him).
- Big Brother Instinct: As the series goes on, Mark becomes obviously very protective of Ryan, and wishes he could take on more of Ryan's burdens for him.
- The Big Guy: Mark is the main fighter on the team if they have to fight human enemies face to face. It helps that he's a jock who's the star athlete in their school.
- Jerk Jock: Mark can veer into this territory, though he's only a jerk to Ryan and his friends. Even then, he's still willing to admit when he's taken things too far, is still helpful when it counts, and does genuinely care about Ryan & the rest of the MECH-X4 crew.
- Jerk with a Heart of Gold: Over the course of the season, Mark learns to be more affectionate and caring to his little brother (and to a lesser extent, Harris and Spyder). Even if he still acts like a dingus sometimes.
- Unmanly Secret: He's into embroidery because of his cosplayer girlfriend's influence.
- Ryan Wants His Jerk Brother Back: When Mark starts acting exceedingly nice to Ryan in the wake of finding out that Ryan is adopted, Ryan ends up having to talk him out of it, at least while their lives are in danger.
Harris Harris Jr.In charge of MECH-X4's defense, confident nerd, one of Ryan's childhood friends.
- Asian and Nerdy: Harris is portrayed by Filipino actor Kamran Lucas. Harris is very skilled with technology and hacking.
- Catchphrase: Several. "Not the time, not the time!" (once "Not the tie, not the tie!"); "Inappropriate!"; "Dang, son!", "— is a beautiful man"; "Science!".
- Distressed Dude: Mark mentions him being one in Let's End This! Part One, using past examples from previous episodes including him hiding from the first monster MECH-X4 encountered, being infected by the ooze, and knocking himself out while fighting goons. His attempts to contest this lead to them getting kidnapped, which leads to him consuming primorphorous gel to escape their captors. Mark realizes that his complaints pushed Harris too far and eventually apologizes.
- Improbably High I.Q.: A freeze frame bonus in Let's Go Clubbing! reveals that Harris has an IQ of over 200 (according to him)
- Insufferable Genius: Downplayed compared to other examples, but he does occasionally get egotistical about his skills, especially when he feels that he'll come out on top as a result. When Ryan once told him he was wrong about something, Spyder was mortified, saying that was the worst thing that Ryan had ever said to Harris!
- More Teeth than the Osmond Family: Harris gets these in his second mutation.
- The Smart Guy: He's in charge on filling the guys in on what to do and how to handle MECH-X4's gadgets.
- Super Speed: Briefly had this when mutated.
- Super Strength: Harris briefly had this while undergoing a mutation before he was cured in Let's Get Some Air!.
- Teen Genius: He's around the same age as Ryan and Spyder but is capable of making gadgets way past his grade level.
SpyderIn charge of MECH-X4's offense, very eccentric, one of Ryan's childhood friends.
- Cassandra Truth: In Let's Get The Big Bad!, Spyder actually tries to tell the police about the villainous plot that the MECH-X4 team are trying to stop. All he gets is laughed at by the police because of a prior prank he lied about not doing. In his defense, he only attempted this just to look responsible.
- Cloudcuckoolander: Trying to fix his own leg with duct tape and believing that stop signs are only suggestions? Sounds like Spyder, alright.
- Cuckoosnarker: Much of his humor is deliberate and as snarky as his friends' can be.
- Hidden Depths: Spyder is able to give a thoughtful critique of the architecture of the Harper Futuristics building solely based on information he learned from magazines. To Ryan's surprise, he's also the first to escape being tied up by Park Ranger Jack, which Spyder explains is because he's "been tied up so many times".
- Spyder is rather intuitive to how his friends are feeling and what their motivations are, but isn't so good at the "trying to comfort them in response" thing.
- O.O.C. Is Serious Business: Whenever Spyder gets either serious and responsible or insightful, you know the situation is dire.
- ...Or So I Heard: When Harris is freaking out about going to prison, Spyder states "It's not that bad".
- Shipper on Deck: For Harris and Veracity, telling them to their faces to "just kiss already", much to their disgust. Although this doesn't stop him from being excited for what he thinks is a date between Veracity and himself in "Versus Harper's Ghost".
- Troll: To distract Harper's monster from causing more destruction and buy time to bring in MECH-X4, Spyder mocks Seth Harper from the ground, using the Bounce Belt to protect himself when Seth inevitably gets mad and tries to stomp him.
VeracityHarris's loathed scientific rival who competed with him for the Harper Grant. She becomes a member of the team in Season 2.
- Ascended Extra: Admitted by the crew as being one before she even premiered. She appears in one episode in the second half of Season One, Let's Go Clubbing!, but has an expanded role in Season 2 where she joins the team.
- Belligerent Sexual Tension: Spyder thinks her rivalry with Harris is this, but they both seem disgusted by the idea.
- Brainy Brunette: Is a brunette and made a miniaturized black hole as her Harper Grant project.
- Has Two Mommies: Gender-inverted. As mentioned in passing.
- The Rival: Serves as this for Harris.
- Sixth Ranger: Officially joins the team in Season 2.
- The Smurfette Principle: She is the only female member of the team in Season 2.
MECH-X4The giant robot used to fight against the primorphorous monsters.
- Humongous Mecha: Obviously. One of the key components of the show. Unlike other mecha shows, the titular MECH-X4 is controlled through Ryan's motions through technopathy with the aid of a harness to facilitate jumping. In practice, control of the robot is similar to virtual reality controls in real life. The cockpit is more spacious than your typical mecha cockpit to accommodate for this, with the consoles that Harris, Spyder, and Mark use to man the weapons being more like computer desks. The mech itself actually has several different areas on the inside, including an entertainment room and a maintenance room. MECH-X4's arsenal includes shoulder missiles, a Plasma Cannon, a Plasma Punch, a Plasma Axe, a Chest Blaster called the X-Weapon, and a drill.
- Motion Capture Mecha: Ryan controls it with a harness strapped on his waist, allowing him to control the mech with his body.
Cassie VineA student at Bay City High who does digital journalism on a YouTube-like site.
- New Media Are Evil: Averted, part of Cassie Vine's character is showing that digital journalism is as valid as traditional journalism. While her investigation into the identities of the MECH-X4 pilots comes close to revealing their identities, she's portrayed as non-malicious and just wanting to find the truth about the city's protectors. This is contrasted with Godfrey, whom sees Cassie as unprofessional competition, using his position to force his narrative about MECH-X4 being evil. It's also contrasted with Seth Harper. He only pays attention to Cassie when it's to his promotional benefit. He's also mad enough about her reporting right in the middle of his final monster attack to strike phones with video capability out of appearing in his "new world".
- Out of Focus: After appearing in the first two episodes of Season One, Cassie finally returns in Let's Handle Our Stuff! to help Seth Harper, who was also out of focus since ''Let's Be Idiots!', promote his new scholarship.
- Punny Name: She's a vlogger with the surname, Vine.
Principal Kim GreyThe Principal of Bay City High, secretly the one behind the monster attacks that hopes to stop MECH-X4 and its pilots.
- Ambition Is Evil: It's implied she wanted to be a part Seth Harper's Evil Plan more to get a position of power rather than out of true devotion to creating a new paradise on Earth, and would do anything to stay in her boss's good graces.
- Big Bad: She's the one creating the monsters that attack the city. While she usually oversees things from the principal's office, while also trying to fit in undercover, she occasionally gets out into the field herself to directly attack, like in Let's Open The Monster Heart!. She also doesn't want to be too cooperative with her boss either, deliberately withholding that she knows Ryan's identity because it can be used as leverage. Thanks to her plans being frequently stopped by the MECH-X4 pilots, she's lost credibility with her boss, forcing her to team up with the pilots to stop the Mastermind's even eviler plan.
- Big Bad Wannabe: At first she appeared to be building up to this, having the ambition to capture Ryan and attempting to earn brownie points with her boss and a position of power, but it's ultimately for naught because she loses face with the Mastermind after her plans keep failing.
- Dark Action Girl: Is competent in combat against multiple opponents and isn't above murder to get what she wants.
- Dean Bitterman: A downplayed example, she hates children and her job as principal, but is exceptionally good at concealing this behind an affable demeanour. And definitely not played for comedy.
- The Dragon: Acts as this to the real Big Bad, Seth Harper. However, she seemingly perishes in the gel, and is replaced by Morris.
- Enemy Mine: Offers to help the team to track the Big Bad so that they can take him down. However, this gets subverted, because it was a trick for them to lead themselves to her boss in order for her to earn back her place. Unfortunately for her, the Mech-X4 crew didn't trust her from the start, and they saw her double-cross coming.
- Evil Teacher: Also not played for comedy.
- The Heavy: At first, she appeared to be the Big Bad because she was creating monsters, but in reality, she was just one of many of the Mastermind's agents. As far plot importance goes, she served as a decoy for the real Big Bad.
- Jerk with a Heart of Jerk: Ryan thought there was some good in her despite her callousness, because she saved his life from the Big Bad's goons. Turns out she was playing the team to sell them out. The team were wary enough not to trust her, and they stop her before she can turn Ryan in. Despite this, Ryan didn't want to believe it at first, and was upset that he couldn't redeem her.
- McNinja: When Grey goes into the field, she puts on the full get-up: a black ninja habit, smoke bombs, martial arts and sais.
- Never Found the Body: Grey falls into a pile of monster goo, leading the team to believe she was dead, but they later find out no signatures (living or dead) have been found in the vicinity.
- She survives and goes on to be the Big Bad for the second season.
- Pre-Asskicking One-Liner: When she and the MECH-X4 crew take on the goons that the Mastermind sent to take her out."Oh no, I'm cornered and I'm helpless...is what you'd expect me to say!"
- Self-Disposing Villain: Grey is seemingly done in by an accident involving her own equipment after a double-cross.
- The Quisling: It's implied that she's helping the Big Bad to be spared by his Evil Plan. It's understandable when that plan is revealed to be to kill off most of humanity.
DavagePrincipal Grey's right-hand henchman and personal muscle.
- The Heavy: Davage acts as the henchman to seed the monsters.
- No-Sell: Davage is capable of shrugging off blunt force and electric shocks.
- The Quisling: It's implied that, much like his boss, he's helping the Big Bad to be spared by his Evil Plan.
- Super Strength: Davage is capable of tearing open metal doors with no issues.
- Torture Technician: Not shown onscreen, but is clearly identified as this. With his enhanced abilities and sadistic attitudes, it's not going to be pleasant what happens to his interrogation subject.
LeoThe mysterious creator of MECH-X4.
- Beware the Nice, Silly Ones: He can be very menacing when he feels the need to be, as "Versus Sabotage" shows.
- I Never Told You My Name: Leo knew Ryan's name in the pre-recorded message that played inside Mech-X when Ryan and the others first discovered it. Then we find out he knew Ryan since birth, and he was the one who anonymously took him to the adoption center.
- Pop-Cultural Osmosis Failure: Type 1: Leo jokes that when he was first captured by the Leader, "Taytay was reintroducing the crop top." When Ryan responded that he had "no clue what that was", Leo immediately felt older than he was expecting because he was referencing something recent by 2017 standards.
- Posthumous Character: Subverted; At first we're led to believe MECH-X4's creator is dead or disappeared, but we find out he's alive and held hostage by the real Big Bad.
- Sixth Ranger: After being rescued, he joins the team.
- So Proud of You: He assures Ryan that his birth parents would be proud of him, and that he is, too.
- What Happened to the Mouse?: He escapes the team in "Versus Sabotage" after Harris frames him for putting a clockwork bomb inside MECH-X4 and has not been seen since. He doesn't even appear in the season 2 finale.
Grace WalkerRyan and Mark's mother, owner of a food truck company.
- Brainwashed and Crazy: In the Season One finale, via a miniature monster put in her brain by Seth Harper to make her his consort against her will.
- "I Know You're in There Somewhere" Fight: Ryan successfully gets through to her and the monster in her brain melts.
- Nice Job Breaking It, Hero!: In "Versus the Betrayal", she is manipulated by a Brainwashed and Crazy Harris into releasing him while Mark was supposed to keep an eye on him.
- Parent with New Paramour: A Type 2: Mark is overprotective about his mom Grace dating new people. When Mark oversteps his boundaries when he suspects that a business trip to Harper Industries was a romantic rendezvous with one of the employees there, Grace stars dating Seth Harper to spite him. In Let's Be Idiots!, Seth does genuinely want to warm up to Mark to reassure Grace. This forms the basis of the B story of Seth trying to get Mark into a sold-out EDM show without using his status as a rich CEO.
Seth Harper/The Mastermind
CEO and owner of Harper Futuristics, a technology company focusing on advanced technology in Bay City. As the Mastermind, he's behind the monster attacks.
- Affably Evil: Even after it's revealed he's the Big Bad, he doesn't see reason to be enemies with everyone. For example, he had at least enough respect for Ryan, Mark, and Harris to be a part of his new world until he learned they were pilots of Mech-X4. When he caught Ryan invading his mind, he was still civil towards him. He even admits to Morris he started using the kids' term "monster heart" because it sounded cool.
- Bad Boss: Has no patience for Grey's failures and is already a hair away from eliminating her. He's not that much nicer to anyone else directly working on his plan who screws up.
- Benevolent Boss: Seth Harper makes it a point during an evacuation of Harper Industries that the employees getting out safely matters more than what they're working on at the time and valued that more than the destruction of expensive equipment. He even knows the name of the window washer MECH-X4 saved in Let's Get Some Air!. Even as the villain, he even had all his followers go into bunkers before launching the missile with the giant Primorphous core.
- Big Bad: For Season 1. He's secretly the mastermind behind the mutant monsters with a plot to wipe out humanity.
- Cool Sword: Gets one of these when confronting Ryan in his own mind, a red blade with dark smoke coming off of it.
- Disney Villain Death: Is seemingly killed with his monster in Let's End This Pt. 2. The control centre in the monster's head was really an escape capsule and was ejected prior to its death with Seth inside.
- Evil Counterpart: Seth created his own monster that works like how Ryan operates Mech-X4—he can bond himself to it, and control the monster with himself as the brain and heart. Unlike Mech-X4, it's entirely biological, so he doesn't need a crew for assistance.
- Evil Plan: To kill off most of humanity with only a chosen few allowed to remain.
- Face Framed in Shadow: His face is never shown. The whole premise of Season 1 is uncovering his identity. "Let's Get Leo!" finally reveals him.
- Greater-Scope Villain: He communicates to Grey and Davage via audio only. In Let's Get Some Air!, we also find out he's holding MECH-X4's creator hostage.
- Heel Realization: By the end of Season 2, after seeing Traeger as a distillation of all his worst aspects, and that the Mech-X4 team are living proof humanity isn't as hopelessly corrupt as he thought.
- Hes Back: He survived the final battle with Mech-X4 at the end of Season 1.
- Hoist by His Own Petard: Harper and his monster are stopped by having the monster heart that was going to be dunked into the huge deposit of primorphorous gel thrown right at them.
- The Man Behind the Man: He is Grey's boss, and he's the one supplying her with the chemicals to create the monsters. However, Grey herself remained unaware of his true identity.
- Omnicidal Maniac: Described by such to Ryan by Grey in Let's Get Our Robot Back!, with world destruction being his main goal.
- Utopia Justifies the Means: Believes that this is the case, because he's disgusted at people's selfishness and their polluting the earth. He feels that by destroying humanity, he can begin anew with one that is clean and free of environmental contamination.
- Villain with Good Publicity: Averted in the Season One finale, where it's stated that he's under investigation.
- Villainous Crush: On Grace Walker, whom he tries to make part of his new world whether she likes it or not.
- Walking Spoiler: And to think, he was so nice.
- Well-Intentioned Extremist: Seth wants to wipe out humanity in order to save the earth because Humans Are Bastards, with pollution, war, and any kind of selfishness.
A sentient being composed completely of red ooze. His goal is to conquer the world.
- Berserk Button: Always call Traeger by his name, he doesn't appreciate being referred to as "that thing".
- Big Bad: Season 2's major villain.
- Flight: He has the power of flight.
- Flying Brick: Has both of the required primary powers to be counted as this.
- Foreshadowing: His first appearance is as a hand forming out of red gel in the final scene of the last episode of season 1.
- A Form You Are Comfortable With: As soon as he is able to become solid, he asks Team Mech-X4 if he has gotten his physical appearance correct to resemble this planet's dominant species.
- Greater-Scope Villain: Is this for Seth Harper.
- Meaningful Name: Traeger means "to control everything/everyone". Since his stated goal is world domination and he personally chose his name, it's likely this was intentional.
- The true significance of his name is eventually revealed when he informs Ryan his master plan is to remove free will and independent thought from every human on the planet, making the population his to control.
- Shapeshifting: In addition to taking on a humanoid form, he can also transform into a Dinoscorpion and a flying fire breathing monster.
- Shockwave Clap: When he attacks a military experimental weapons research facility, he uses this power against the guard squad to knock them down before:
- Super Speed: He runs at the squad and defeats them all using unarmed combat in less then a minute.
- Super Strength: Is strong enough to hold up Mech-X4 when it stomps on him and then tosses it away like it weighs nothing.