One of my friends on DeviantArt really helped by encouraging me to finish this. Again, not quite up to snuff with Parasite Eve's original abominations, but I still like it. Like my NMC-Pikachu, I've listed some information about this creature below!

--Eevee is already a fairly unstable Pokemon in terms of its genetic code. The NMC-Eevee is also highly unstable and is basically a more violent evolution of Eevee. Only one NMC-Eevee exists. If it were present in the Parasite Eve games, it would be a mini-boss of sorts.
--Upon mutation, it grows absolutely massive in size, becoming five times larger than a normal Eevee.
--It can survive in just about any environment due to both its unstable genetics and highly-evolved mitochondria.
--The fur around its eyes, hind-paws, and tail have fallen off during mutation, leaving some nasty-looking, diseased skin.
--Mitochondrial fluid can be seen pouring out of enlarged pores on its tail. Touching this goo is not a good idea, as it can infect just about anything, from animals to plants to humans. The NMC-Eevee is also shown to have this fluid excreted from its mouth.
--Due to its extremely violent nature, the NMC-Eevee is usually not seen near other NMCs. This means that if you meet it during battle, you'll be fighting it one on one. Be prepared for that!
--Due to how horrifically altered in design and structure it has become, the NMC-Eevee cannot evolve into any of an Eevee's higher forms (Flareon, Vaporeon, etc.). Not that it really needs to, considering how powerful it has become.

Here is what Eevee normally looks like: http://cdn.bulbagarden.net/upload/e/e2/133Eevee.png