mane mane no mi: it would be great if it didn't just work with players, being able to copy the appearance of mine mine npcs and being able to pass between them without being detected (obviously from the same side)
some debuff could be if you add that you detransform if you receive some kind of damage
silent silent no mi: you could make it so that entities in a certain range can't "see" you, since you go unnoticed
suke suke no mi: true invisibility, basically that mobs don't attack you when you're invisible, you can add that they see you if you do damage to them or make some kind of noise, such as breaking a block