I think the new boss from the recent april fool's event is pretty cool. He isn't too hard to beat and does some neat things like inflicting defence loss so he can have an easier time landing hits on you, especially for later when he gains the berserk status so he can hit even harder on his SP attack.
You also gain berserk so you do more damage but lose BTH, the latter part ends up not mattering anyways because I have an auto hit ice weapon.
The main thing to worry about is the burn stacking from the boss, if you allow him to keep stacking the burn, it can end up doing a lot of damage. So I use a +10 resist burn shield and frankentwilly guest for status resistance, and hoped it was enough to resist most of the burn attempts. If you're a mage you can also use the cold sore weapon which gives +20 burn resist. I also used the optic misc, the bth boost doesn't matter to me but it had a cheaper SP cost than cyclops eye.
I could've trivialised this boss by going into a FD fire armor + baby egg, and use protocea misc to cleanse the burn, but I thought that was boring so I decided not to do all that.
Music used:
Etrian Odyssey Untold: The Millennium Girl - Decisive Battle: The End Of The World