You can play Merc Zone in a99.io as unblocked.
All you have to do in the Merc Zone game is that you have to destroy your opponents alone before the 4 minutes is up, and you have to get the most points among your opponents before the time runs out. There are weapons named Brock, Cochese, Crazy Ed, Bingo and Ogre that you can change. It can move with "W, A, S, D" Keys. You can shoot with "Left Click" Key. After you die, you can be born again and again.