Pearl

An evil white dolphin with a penchant for making weapons of mass destruction, fake eyelashes, and a black pearl necklace. She took over the Sea Ninjas after their previous leader kept failing, only to have her plans foiled by Luka, who turned her own weapons against her and (accidentally) got her eaten by sharks.

My favorite detail about her is that she built a wheelchair for getting around on land, and it was purposely made taller than necessary so she could look down on people.