My idea is pretty crazy:
Bubbles is a fishman and he has parasites in him that do damage.
E: Shimmy
He throws a large worm in the sky and as it flies it detects people.
C: Barnacle
He has 2 of these barnacles and when someone walks over them he is delt 50 damage
Q: Sea Weed
He place a wall of sea weed and vision is blocked by it. If enemies push it they take decay for 2 seconds and they are blinded
Ult: Sea World
He covers a whole area with water and fish swim around dealing damage to those hit by the fish. Once the ult ends everyone inside the area takes 50 damage. The ult lasts 15 seconds