It's easier to do this on lower difficulties as the fly effect is substantially decreased at higher settings making it harder to send opponents flying.As there are not enough bandits to get the achievement in one round at both locations, once you've killed everybody, teleport to another map then come back to the area and the bandits will have re-spawned.Don't bother trying to do this with 2-handed vagabond, as you can't send him flying. Lure them on top of the cliff, stand near edge, wait for one of the 1-handed bandits to attack, then sidestep and Aard him flying.

If you already finished In the Eternal Fire's Shadow while getting the good ending (friendly NPCs move into the Pit), one alternative might be Herbalist's Hut.

You may need to repeat this several times before they'll actually die, depending where they land. Simply lure all the bandits up to the higher platforms, having them as close to the edges as possible (parrying helps), then use Aard to blast them over the edge.

An easy location to do this is at the Devil's Pit.

The Witcher 3: Wild Hunt Humpty Dumpty is an achievement in The Witcher 3: Wild Hunt and requires one to kill 10 opponents by knocking them off somewhere high with Aard.

Overkill achievement guide witcher 3