This achievement requires that you earn the highest distinction from power combos. Distinctions are earned when you kill a large group of workers quickly in succession and are recognizable by large yellow-lettered words that pop-up on screen. To earn higher distinction ranks, you must keep your current combo running while earning numerous distinctions. There are 6 ranks of distinction. In order, they are Punishment, Annihilation, Cataclysm, Armageddon, Judgement Day, and Apocalypse. To further clarify, you must kill a large group of enemies (usually 4-8) quickly to earn the Punishment distinction. Keeping your combo maintained the entire time, you must earn a distinction 5 more times until you reach Apocalypse.
Level XI of Campaign is a good one to attempt this on. Right from the start, you constantly get bombarded with waves of enemies. You should definitely equip the three star version of Combo Spirit for your passive power which will increase the combo timer to help you maintain your combo to reach the highest distinction. I would also recommend using the fully-upgraded Wind power in combination with either Earth or Water. Earth's Crush power and Water's Rain power are both weak but can be used frequently and are good for maintaining a combo. As soon as you earn your sixth distinction in the same combo, the achievement will pop.