Having just gotten this achievement (after trying for this in Tower of Doom and basically getting only 4) in Shadow Over Mystara I can say it is extremely easy to nab with the Magic User.
I chose the Magic User in chapter 2 Village of Trintan. You will start with a Fire Wand and also an Ice Wand. Equip the Ice Wand immediately and group up the enemies as close as possible. Hit them with the actual Ice projectile the wand shoots and they will freeze and fall to the ground. I walked over the top of them and mashed the A button as much as I could. If grouped together properly you can hit multiple enemies multiple times and nab this achievement in the span of a few minutes! I had to much trouble in the Tower of Doom trying this with the Fighter and got basically nowhere. This makes this achievement a joke and one that you can earn easily if you need an achievement to keep a streak like I did!