Unleash

Unleash is a keyword ability that was introduced in Return to Ravnica as the mechanic for the Rakdos guild. 
==Description==
The reminder text for Unleash reads "You may have this creature enter the battlefield with a +1/+1 counter on it. It can't block as long as it has a +1/+1 counter on it.".
After being last seen in Dragon's Maze, Unleash was reused on the Murders at Karlov Manor Commander card .
==Rules==
==Examples==
==Rulings==
*You make the choice to have the creature with unleash enter the battlefield with a +1/+1 counter or not as it's entering the battlefield. At that point, it's too late for a player to respond to the creature spell by trying to counter it, for example.
*The unleash ability applies no matter where the creature is entering the battlefield from.
*A creature with unleash can't block if it has any +1/+1 counter on it, not just one put on it by the unleash ability.
*Putting a +1/+1 counter on a creature with unleash that's already blocking won't remove it from combat. It will continue to block.
==Trivia==
*One variant of the acorn has unleash.
* grants Unleash to other dogs.
==References==