Clone Drone in the Danger Zone

The way to do this is to let the enemy robots get killed by the level hazards. The earliest level with hazards is Chapter 1 - Level 2, which has moving sawblades in the ground. Stay on one side of the blades while avoiding the enemy robots, and they'll run into the blades and eventually die on their own. When the round ends the achievement should pop.

A fast way to get this done is to enter the Kick Only Challenge and use the spikes in the middle of the first level to make the enemy impale itself. Don't kick the enemy into the spikes, just run around the spikes until the enemy walks into them on its own.