Killers a tricky son of a gun, bro got weird biology!
Killer isn’t just a monster anymore.
From the way the creator treats him, he’s something in between — part monster, part human. That’s the only reason he can survive with the amount of Determination flooding his body. A pure monster form was never meant to handle that much DT, and his is already breaking down because of it.
Outwardly he still looks mostly the same. The real changes are internal and progressive. Determination is leaking through his joints. Parts of him are slowly turning into a mixture of DT and dust as his body starts to fail. Because he now has living, organic (human) components, he can actually die of old age — something regular monsters don’t have to worry about.
The only way he keeps resetting the decay is by killing and leveling up. Every kill buys him a little more time. He’s basically in the same unstable category as Gaster’s old experiments, only worse. Physically he’s even less stable.
He still wears the same clothes. Part of it is habit, part of it is that, on some level, he still wishes he could stop. When his emotions are dulled he uses that same familiarity as a weapon — reminding other Sanses that he’s one of them, just to twist the knife.
Because he’s treated as both monster and human, the normal level cap doesn’t apply the same way. Theoretically he can push past what most humans or monsters can reach — up to LV 40. The human side gives him physical strength no normal boss monster can handle physically but there would still be some senses that are stronger than him physically.
On the monster side:
His bones can grow larger than anything other senses has shown.
His Gaster Blasters can reach the size of roughly four normal ones combined. If he goes all out, they can fully detonate.
His gravity magic is strong enough to crush someone instantly or fling them into space. At its peak it might even form black holes.
The reason his powers feel so destructive instead of flashy or playful is simple: because of how high his level is and the determination. even though personality wise he doesn't fully want to kill and isn't driven by some murdering Instinct like he may try to betray as he's masking so that he doesn't actually feel all the pain and guilt he has.
That emotional instability, combined with the sheer amount of Determination and LV, means his magic often erupts violently whether he wants it to or not. It can backfire on him or on anyone near him.
And here’s the real trap:
If he stops killing, the decay wins and he dies of old age. If he keeps killing, he eventually hits his maximum level… and still dies of old age.
He’s locked in a loop he can’t escape, all because of the deal he made with Chara.
