I unlocked this achievement on a bull rider, but you will be able to unlock this on any enemy that has a fair bit of health. You need to use at least four different spells on one enemy. Hit it with your lightning, an indirect fireball, push/pull it, then finish with your shard spell. You can do this in any order but I would suggest this order since the shard spell is quite strong and the monsters might not last long enough for a fourth spell if you try another order.