The way I did this was starting a 1v1 skirmish against an easy AI.
Skulls: Pain train, Bountiful Harvest and Emperor.
Options: Fog of war OFF, unit ability cooldown 200%.
AI Leader: Doesn't really matter, I chose Yapyap.
Map: Doesn't really matter.
To get this achievement you will need to make kills with the new Mega turret. Pavium can build these at any of his bases and minibases. Since the gamemode is strongholds and the fog of war is turned off, you can build all the minibases on the map. Each minibase will come with 3 buildings build already, destroy these. Build 3 Mega turrets at each minibase.
Now just sit back and watch them destroy everything. You will get this achievement pretty quickly.