Boss: Aqua Jelly
Attacks: Aqua Giga Blow, Aqua Giga Wave, Recover Body
For this battle make sure you have the following people with you: Karin, Bulldog, Sasquatch, and of course, Atsuma. Next with Bulldog use Reverse Bite. With Sasquatch use Giga Charge + and with Karin use her EX thing if you can. Astuma should die (on the outer edge) along with Bull dog. Once this happens just use Sasquatche's Ice Giga Blow and Karin's EX attack if you can, if not then use her other water attack. Real Easy Achievement if you follow these steps.