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Description: Defeat the mutated zombie plant in Story mode. (Secret)

How to Earn: This boss is on Mission 20 "Operation Lawn Mower".

The mission isn't very hard at all and is unmissable.
Simply kill the boss, drive to one of the waypoints to pickup a bomb, and return to the boss. After placing the bomb the achievement should pop.

Boss tips:
Scout the area for a few seconds so you know where all the health spawns are. You should only need 1-2 but they eventually respawn so don't worry about it. Pretty much any weapon is effective against this boss, just make sure you've upgraded all you can.