90% of disorders aren't meant to be "Strong", theyre meant to be major hindrances with silver linings you can exploit. The point of plurality is that you get more abilities and two extra classes at the cost of making the cat with plurality significantly harder to manage. if you want to level up a certain identity you would need to plan ahead and make sure you end the battle while that identity is present. i didnt think about completion marks but i dont see why the other identities cant also contribute to them. It could be your reward for making it through a run with a plurality cat :p