Board Thread:General Discussion/@comment-35821564-20180803203909/@comment-28802873-20180804090842

Aggregor was insane, he just kept it more under control, like Mike did. Kevin doesn't absorb more aliens, because he's scared. He's scared to go back to becoming a monster, he's afraid to fall back into that state and hesitates about absorbing energy. He doesn't want to be a monster again, and because of that, he chickened out on doing it.

You also gotta remember that while Aggregor merged with five aliens, Kevin absorbed all the aliens unlocked in the Ultimatrix, Ultimate forms included. That's even more than what he absorbed in OS (not to mention Ultimates aren't naturally kind), and considering he didn't do it often, he succumbed to the power addiction again. He also now knows more about Gwen's mana, he tries to absorb it too when he gets the chance, becoming like Darkstar because of that.

It took nearly one of his last appearances in OV to finally get the hang of it without losing his mind for good, and the next times he appears, it's at Gwen's school, where there's more magic stuff than alien stuff (and while he's used to absorbing aliens by then, it'd be a bad idea to try with mana right now if he doesn't know whether or not he can keep it clean with raw pure energy). The Omnitrix also wasn't made for Kevin's powers, he could damage it if he keeps absorbing the energy from it.

Experience also doesn't ensure he'll keep himself under control, Kevin 11K is proof of that. At some point in the future, he'll go crazy again