Some characters in FARTS transformed over the course of the series, so I decided to also add a little section detailing these a bit more.
Name: Mirai Macc
Explanation: A future form of Macc who doesn't speak much, and when he does, it's in Japanese. Macc's was somehow able to transform into his future self, but exactly how he gained this ability is unclear. Exactly why he can't do it anymore in his upgraded form is also unclear. Mirai Macc is unbelievably powerful, but all business, and thus not nearly as likable as Macc. Another version of Mirai Macc came from a parallel universe once, but he didn't have any powers whatsoever, he just wore a fancy outfit; in that universe, Macc is a pro wrestler.
Name: Neo Dark Macc
Explanation: Dark Macc decided it would be cool to have an extravagant transformation like most villains do. When in this form, he is much more powerful (duh) and can apparently destroy Macc without destroying himself. Needless to say, Macc made sure to write in his contract that he couldn't transform anymore. Gee, anyone else who thinks that clause won't last forever?
Name: Super Saiyan Vegeta
Explanation: When transformed in his Super Saiyan form, Vegeta's even more powerful than he already was, plain and simple. There shouldn't be much that can stop him in this form, and yet he keeps running into people even stronger than him, which aggravates him to no end.
Name: Exdeath (tree form)
Explanation: This is Exdeath's true form, that of a tree. Yes, that's right, a tree. And if you don't think that would be very impressive... well, you're right, it's not. He's just a heck of a lot uglier in this form.
Name: Gilgamesh (demon form)
Explanation: And here we have the true form of Gilgamesh. Sure a lot cooler and more impressive-looking than his former boss' true form, isn't it? Just too bad that while in this form, he usually wields a cursed sword known as "Excalipur" or "Excalipoor", which hardly deals any damage at all if you slash someone with it.
Name: Cats' holo-image
Explanation: This is not actually a transformation, but rather a close-up holographic image of Cats. The signal it is broadcast with somehow spreads Cats' speech disorder.