Red Tide

Flash, Islandwalk, Menace
Red Tide costs {x} less to cast where {x} is the
number of attacking creatures.
When Red Tide enters the battlefield it deals X
damage to each attacking creature without
islandwalk. For each of those creatures that dies
this turn, put a +1/+1 counter on Red Tide.
{1}{u}{r}: Return Red Tide to it's owner's hand.