Yeah, I just ignore the chest for the most part, as it is a Mimic after all. As for Ultima and Omega, I find them to be pushovers. Not bragging, but against Ultima I was just getting started with each of my characters getting in an attack and it was dead before I even had all them participate. Omega was the same way, although I had to fight him twice because I forgot to Lancet him to get Nova. I hear you can get Nova from Nemesis too...dunno if it's true or not though.