i heard this from a friend, but Misuto is being revamped in P4R to have extra content and a "link episode", it's not as substantial as the P3R link episodes. his boss fight changes depending if you did it or not to gain extra weaknesses if you did complete it, doing it before he kills King Moron gives an extra scene at the end of the game. King Moron also has a linked episode, but it doesn't change anything.

his new boss fight is mostly the same, his hero form gains more resistances but his baby form has more weaknesses, mostly to any aliments, and is more unstable in it's attacks being multi hits that hit the party randomly. there is secret dialogue if you have yukiko in the party and make him charmed for example. another if he gets put under rage with kanji in the party.

a big focus overall for P4R is adding elements/characters from the two animes into game. doing the linked episodes gives a new unique persona for fusion, and Misuto's gives an 8 bit version of Amanojaku from smt1.