Kill two robots with one
whirlwind, the trick is you can equip more than one whirlwind and use one after the other!
How I did it: I used other augments to make my life easy
2 Whirldwind augments
I went into Tournament 1 were all robots have 5 health, turn myself invisible and waited for 2 robots to be near each other, then I teleported near them and used a whirldwind lvl 3 (which does 3 damage) this will leave the robots with 2 health, I just used a second whirldwind to finish them off.
This video is the exact time I got the achievement.