Gorebyss, to me, is a must have in this one. Although other generations haven't stated this about Gorebyss, it's actually pretty good at attacking and killing it's prey. Figures that only the generation it's debuted in actually says anything about it.

[Quote=Ruby Pokedex]Gorebyss lives in the southern seas at extreme depths. Its body is built to withstand the enormous pressure of water at incredible depths. Because of this, this Pokémon's body is unharmed by ordinary attacks.[/quote]
(Yeah, we're not doing this "Can't be harmed by ordinary attacks" thing. That's ludicrous in a setting like this.)

[quote=Sapphire Pokedex]Although Gorebyss is the very picture of elegance and beauty while swimming, it is also cruel. When it spots prey, this Pokémon inserts its thin mouth into the prey's body and drains the prey of its body fluids.[/quote]

[quote=Emerald Pokedex]A Gorebyss siphons the body fluids of prey through its thin, tubular mouth. Its light pink body color turns vivid when it finishes feeding.[/quote]