Chaosic Rune/YMMV
- Complete Monster: Death Rex. He makes no attempt to hide the fact that what he really wants is to consume everything. That means everything, everywhere, everywhen. The only reason he can't is because he's incomplete. And the only thing keeping Death Rex under control is the hero's willpower, and that fails at least once during the series, with nightmarish results.
- There are quite a few others as well - like the dragon card-user who happened to be a Serial Killer whose kick was cutting off people's faces while they were still alive (and his main monster's special ability was to make any surface he could visualise frictionless, for example the inside lining that attached the face to the bone underneath... Ew). Or the bandaged machine-card user who's the Token Loli's older brother, who murdered their parents because they found out about his incestuous, pedophilic, stalker-ish obsession with his little sister, who mind rapes her so she'll be Brainwashed enough for him to control her for the rest of her life. And then there's the Magic Clan- virtually every magic(monster) card-user seen commits atrocities purely For the Evulz, and of those, the ones with more screentime and characterisation than a Mook all display a complete lack of redeeming traits. Only three plot-important Magic Clan characters are even remotely likeable- one is actually not even human, but a magic card-monster who's equal parts Blood Knight, Colonel Badass and Worthy Opponent, the second is a little girl who's obviously in over her head and has fallen in with the wrong crowd, and her surrogate father-figure who's also a Blood Knight Worthy Opponent (both serve as each other's Morality Pet). And the last two only appear in the sequel series.