Go to the Devil's Pit area of Velen. After entering the camp, use the stairs to throw people into the pit. Lure to the edge of the stairs, then cast Aard to knock them down. Kill any enemies armed with the two-handed weapons, as they cannot be tossed easily. After the camp has been cleared of enemies, fast travel out of the area then return to the Devil's Pit fast travel point to respawn them. Spending 3 points in the first Aard upgrade, Far-Reaching Aard, may be useful as it will the spells range by three yards.