Ok, so, I was playing goat MMO simulator, when i got this crazy idea: what if there was a map of the Underground from undertale, but all the monsters were goats, and you were a human?
This would require several mods to work: first there would need to be a mod that replaces your charactwr with a human, second there would need to be mods for each major character, third there would need to be AI coding for using special abilities, and possibly a mod to emulate determination. Also the map would need to use MMO simulator's quest system to make it play like an actual game.

Now, with all that said, if anyone actually wants to undertake this project, I have a few ideas for the monsters:
Toriel's mutator would be a white goat with a purple robe, and pressing R would shoot fireballs like the magician mutator. 1 spawns pie
San's mutator would be a blue jacket and a gaster blaster skull over the head. 1 fires blaster beam from mouth, M1 shoots bones, E doesn't have a tounge but instead makes target glow blue, and R teleports.
Papyrus's mutator would be a red scarf and boots, and of course a skull head. M1 fires bones, though they jut up from the ground and move forwards rather than just being flung. R does his special blue attack. 1 spawns spaghetti.
Undyne would actually have multiple mutators:
Main mutator is eyepatch, armor, and possibly red hair. M1 fires spears, R makes target glow green and become unable to move, only turn, and of course gives them a shield. Effect fades after a period of time, or can be canceled by pressing R again. If HP hits 0, yu can still fight for abbit.
Undying mutator is similar, but instead of an eyepatch you would have the glowey-spear-eye thing. Everything else is the same, but you'd have more HP.
Alphys mutator is just a lab coat and glasses.
MTT's initial form could just use the robot mutator, as he doesn't really try to attack you in that form.
Mettaton EX would be a robot goat skin, pink boots, and stylish black hair. R summons mini parachuting robots that drop toss bombs at nearby living creatures.
Asgore would be a crown, large horns, and purple cape. R would shoot fireballs like Toriel, and M1 slashes a trident. Goat would also be larger.
Flowey would not be a mutator, it would need to be a scripted prop. Same goes for nightmare flowey.
Asriel Dreemurr would of course have long horns and the black streaks on the face. Also a purple robe. Leaves a rainbow trail and flies. M1 is chaos sabers, 1 is shocker breaker, r is star blazing.