Well attack wise you can go either Sharkbomb which literally locks down your opponent or use the Water Punch mystery (although I don't use it outside of Zenith).

Also don't underestimate Poison Tai. I know not many people use Water Main with poison tai in the late game but in mid game it wrecks any teams that aren't immune. If you have the right ninjas to go with it like Fuguki or something you can shred a lot of team very easily.

Healers in general are extremely weak in the game.

Mains are not used for offensive purposes (pos 1/2) in the end game. The worst main right now is (and has been for quite some time) Lightning Main.