Depends really. You could call it mutate (or whatever) and it would seem Simic. Sort of like.
If X would die instead exile it and create (whatever power/ability).
It's probably more golgari than simic still, but simic's wheelhouse of +1 counters is boring anyway.
Edit: Or maybe even a trigger on death where you pay mana and it comes back bigger or such. Or some kind of Skaab Ruinator where you exile two creatures to create a token. Like each one has mutate and you exile them from the GY to gain both abilities.