The way I done this achievement and possibly the easiest way was I got Lightning and Magic Gambit both to 50/50 and did Stage 1 on Normal. You'll have to be very careful though because if you over-use your Lightning, meaning you use it once you've killed an enemy, the Lightning strike will hit you and take away health, voiding the achievement, if this happens, you'll have to restart the stage, but I'll tell you have many hits it takes for each enemy to kill;
Williams - 1 Lightning hit.
Linda - 2 Lightning hits.
Abobo - 3 Lightning hits.
I also did the same for the 'Misters Perfect' achievement, but since it had to be done on Double Dragon difficulty, it took more Lightning strikes to kill the enemies on the stage as well as keeping my second controller out of range or being hit by enemies. I can't give you exact estimates of how many hits they'll take, but all I can really tell you is to take it slow so you don't hit yourself with the Lightning.