Return to Ravnica new mechanics Explained (Part 3 of 5)

Unleash
The unleash mechanic allows you to have a +1/+1 counter on a creature as it enters the battlefield with the downside which is not being able to block with +1/+1 counters on it.

This mechanic is designed to allow your creatures entering the battlefield a little bit stronger if you plan to just attack. But in the case of Grim Roustabout you can also opt to let it enter without +1/+1 counters and be a strong blocker with regenerate.
 Just like Overload it doesn't make it better than a specific defensive creature to defend, or a specific offensive creature to attack, but gives you the choice of being a decent defending OR attacking one in just one card.

 In my next post I will talk to you about the mechanic scavenge.