[Wrana]

Crocodiles I'll also vote for! I wouldn't say they should entangle, however - this could be left for some separate units (sea snakes, coralls, etc.). But crocodiles have a nice habit of using their tails for leg-breaking attacks - which would also be painful for enemy thugs.
Also, we could dig into actual Oceanian mythology, as the name itself suggests (unfortunately, I'm not good in that, but I'm sure we can dig out something interesting).
I do not think that they should have their best units made better on land than in water, though - something else must be found.