Two Worlds II

Very easy, although it will take some time if you want to unlock that one early on. Simply finish 50 enemies with a magic spell (equiping a staff of course). You can always hit enemies with your sword or bow before finishing them off with the staff.

You can keep track of your statistics by pressing B (when no weapon is equiped).

I found a surprisingly quick and easy way to do this if you are a high level and have been ignoring magic throughout your run through. I was around level 40 when I did this for a reference point, but I really think you only need about 30-40 skill points to do this quickly.

First head to one of the soulpatchers in the cities. I used the soulpatcher in the University in New Ashos. It costs 500 gold to reallocate some of your points. Do it as many times as you want, but as stated before, have around 30-40 points to spend in magic.

Spend
+8-10 in a school of magic of your choice, preferably the school in which you have the most effect cards for. I found that the necromancy was the most common as there are many "shady" citizens throughout the cities who sell only daggers, traps, lockpicks, and necromancy cards.
+8-10 Wisdom which affects how many modifier cards you can apply to a spell
+5-10 Talented Tongue affects casting speed
+5-10 Summoning if you prefer to create magical traps or summon minions, which stacks for the achievement


The next step is only recommended if you do not have a lot of cards in your inventory: Fast travel to the major cities with vendors and buy up as many cards as you can from the magic vendors and "shady" vendors.

I was a little surprised at how cool some of the combinations are that can be made with the modifier cards. For example, if you stack as many necromancy decay cards combined with missles and modifiy the spell with ricochet, you can decimate pretty much an entire group of low level animals in the Savannah. For the purpose of this guide I recommend creating a spell which has as many of your spell effect of choice on it. You can stack up to 10 cards if you applied 10 skill points into your choice school of magic. Combine that with the Area of Effect effect card and apply time, damage, and protection modifiers to the spell. My end result was something like 357% of the damage done to my character was reflected back as fire damage and the spell lasted 118 seconds.

Obviously you won't have the same cards as I had so play around with what you come up with. Then find an area on your map that you haven't really explored much (or know you did not kill a lot of creatures there), apply your reflection or area of effect spell and just let the low level animals in the Savannah (or other area of your choice) just touch you and die. It was quite amusing. I racked up 50 magic kills in just short of five minutes and my area of choice was the Savannah south of Bayan.

I hope this helps and please leave a comment if you would like to downvote so that I may improve this solution for others. Thank you and good luck! :)

Following on from Ryowebo....

The easiest way to get this is to head into the off-road areas around Hatamandor. You can often find packs of animals like hyena, wild boar and so on, There are plenty of them and they are way easy to kill. I'd take a swing or two at a beast and then finish it off with a fire-based spell.