I always wanted an underwater X-men team/strike force since Utopia... prepared for attacks under the island but are there enough amphibious or water-based mutants to make this happen?
Namor
Namorita
Transonic
Sharkgirl
Iceman
Hydro (if alive), Squidboy, Fish can make an appearances...
Maybe add mutants that do not need to breathe... Rockslide?