|“||I am the one, who's creating the monsters.||”|
A monster is a creature created to destroy Mech-X4 and the team, but it's especially created to destroy Ryan Walker, the pilot of the robot. Monsters have been featured in every episode since the first, and it's possible they will continue to do so in Season 2.
- Unnamed monster (created by Principal Grey)
- Harris (temporarily)
- Harris started turning into a monster after Let's Call It Mech-X4!, due to accidentally drinking monster ooze.
- No monster was featured in this episode, since the team was trying to open the primorphous core, and Grey attacked them in trying to get it back.