After beating level under 13 minutes mark you get to choose one of 3 portals:
- Blue: end the game
- Red: start the Overlord cycle
- Purple: start the Endless mode
Enter red portal, run through new waves of enemies again, enter the next portal to the Overlord Cycle 2, then fight all enemies until next portals, choose red one again into Overlord Cycle 3. When you defeat all enemies on Overlord Cycle 3 you can go through any portal to obtain this achievement.