Can be used if "Umi" is on the field, and you have a Water-attribute normal monster on your field. That monster can attack your opponent directly. this turn. At the end of the Battle Phase, that monster is sent to the Graveyard. This skill can only be used once per turn.
I've been running this skill for awhile, and it's finally gotten some great support. Birthright, Warrior of Atlantis, and Swamp Mirrorer are some great cards to use with it. As for monsters to use, Gagagigo and Giga Gagagigo are best.