Sea Critters

Make {x} number of 1/1 sea critters, they have swimming (deal double damage to octopus, leviathans, krakens, serpents and merfolk).
Put a counter on Sea Critters, for every octopus, leviathans, krakens, serpents and merfolk played add 1 to the counter and make
1 creature with X/X where X is the counter
on Sea Critters.