Well, I actually decompiled both AnimationAPI and Mutant Creatures with Bearded Octo Nemesis (BON) and Luyten, and I ported AnimationAPI successfully to 1.12.2 by fixing almost all of the errors. However, we might want to get into contact with thehippomaster21 to see if it's okay to port both mods to 1.12.2 or not.
Nice to see someone porting this mod, but still permission is required...
How about making an unofficial one? :3
I'd honestly be for a port/continuation of the mod. I'd love to see some reworks of the Mutant Skeleton, Zombie and Creeper to have them more on the level of Mutant Enderman's quality, and of course some new mutants because it'd be sick to see a Mutant Blaze and Mutant Wither Skeleton.