River Coral Fluidling

Hexproof
Whenever Coral River Fluidling enters the battlefield, each player mills four cards. Exile a creature from a graveyard. You may have Coral
River Fluidling become a copy of the exiled
creature, exept it is a blue green creature with hexproof, haste, and "At the beginning of each
endstep exile this creature then return it to the battlefield."