This achievement requires that you defeat 100 A.I. enemies in the game and is cumulative across all plays of all saves and worlds. This can quickly be obtained by inserting the max amount of enemies into an empty world. When in a world, tap the paint brush button in the top right corner of the screen. Then, in the bottom bar, select enemies. You will only have two options of enemies to add in the Windows 8 version, the Soldier of Clubs and the Soldier of Hearts. Tap, hold, drag, and release the enemies into your world until your reach the maximum and then exit back to your world by tapping the red "X" in the top right corner. Kill the enemies using the attack buttons. When you kill the last enemy, add them again and repeat (approximately three to four times). As soon as you kill the 100th enemy, the achievement will pop.