I'm not asking how to get through or defeat the bosses per se. Just a couple of questions:

1) Will undertaking this dungeon prevent me from getting the Mascot Dressphere if I don't get through all the levels? Can I still avoid this dungeon completely and get the Dressphere anyway?

2) If I'm trying to collect Oversouled monsters of every species, should I not go deeper until I get the Oversouled monsters for each level?