During the course of the game, you may turn choose to become (or get cursed into) one of five animal forms that currently exist within the game.
These forms, while they limit what you can do in many aspects, give you access to special animal-only skills.
Some forms, like Cow, can be reversed by defeating the boss that cursed the player. Others like Deer, Pig, and Spider must be reversed by the consumption of an 'Un-(animal) Juice'.
Lycanthropy is permanent in a sense; you have a skill that will allow you to transform from werewolf to human and vice-versa, but you will be locked into your werewolf form on a full moon.