To my defense, if i recall correctly, cat wasn't implemented in game when i posted this card. And for this card, I mostly had mono death in mind. It doesn't replace cat because *its permanent *its death card *can be used multiple times *actually kills a creature (getting rid of AM'ed creatures etc) *heals yourself *makes you draw a card instead of doing nothing like cat / giving quanta like immo.
With cat, you don't lose any creature but with necro you draw a card much like gaining quanta with immo. Immo, cat and necro have different purposes with some uses which may intersect. They also have different elements and types (spell/creature/permanent). And if you compare its Bone Wall / vulture buff, i would ask why is Cat implemented when we had OE (or any damage card) which can do the same.
So other than triggering a death effect, its very different and doesn't intend to replace immolation nor the cat. The ability to kill your own creature doesn't have to be unique to two cards (immo&cat), both of these cards trigger death effect they are not alternative to each other. Think of the variety of implemented cards that can kill opponents creatures, there are like what ? 6-7 different cards for it, which by the way, can kill your own creatures multiple times too, like OE.
People didn't mind having lightning, shockwave, ice/fire lances, drain life, RoF, OE, rage pot etc. They have differences and similarities. Necro too has differences and similarities with direct damage cards as well as cat & immo. I could say the same about healing cards and damaging shields.