Inundation should have creatures underwater untargetable? Dunno if that's been suggested before >.>"
This even if it has been suggested before (idk) is a good buff.
Cards should be worthwhile on their own or with a large number of other cards (animate weapon).
As such synergy is not the answer buffing the original card is.
There are two ways to buff the original card either a direct buff like funerallaughter's idea or altering the metagame such that this card becomes much more useful as creature control.