What about someone like Larissa or Selina, who don't have as much anger?
Larissa - Since she's still a human, comparatively little, actually. It'd probably force her into her other personality though, temporarily making it dominant.
Selina - Since she's a ghost, and ghosts are about the most susceptible things ever to being corrupted by negative emotions...
Well, we've discussed what would happen if she suddenly got an infusion of Malice.
It ends badly most likely.
The fox wouldn't be Trying to control it. It would be Digesting it. Malice can't Alter Anything while it's being Eaten. Nothing can Touch the inner aura without shit starting to get exponentially more explosive. You'd end up with a recursive loop of feeding until either one of them decides to warp away, likely with soul altering effects for both or everything Explodes.
... let me put it like this.
Your foxfire is the equivalent of a firework, just for example.
The equivalent amount of Malice is essentially the Czar Bomba in comparison.
if you try to digest an amount of malice large enough to produce much foxfire at all from its raw emotion, it would be enough to at least mutate you, if not outright
kill you. And considering you're a spirit-type being and it's a type of energy that is specifically good at corrupting spirits...
Well, in that case, I guess Plutarch can safely nom on him then Considering it is powered by rage, constantly in rage and able to maintain a facade in spite of it.
Honestly my headcanon has him already using it. A LOT of monsters like that do in the canon it's from, so why not him and creatures like him? He's just not MADE of it and doesn't have the sheer mass of it that Tor does.
Basically it's the difference between having a furnace that burns it to power other stuff and, you know.
Being a star.
The problem with him isn't that he's not powerful, it's that it's physically impossible for him to USE it in any way even remotely useful.
Even in combat, since at the point he's using enough to do extensive damage he can't exactly aim very well.