Other Merfolk creatures you control get +1/+1. : Target Merfolk creature can't be blocked this turn.
"Be like the sea: flow around that which is unmovable; for everything else, crash into it unrelentingly."
Official Rulings for Merfolk Sovereign
10/1/2009 : To have any effect, Merfolk Sovereign's activated ability must be activated before the declare blockers step begins. Once a Merfolk has become blocked, activating Merfolk Sovereign's ability won't change that.
Others who bought Merfolk Sovereign also bought...