If you aren't against mods there is already a custom version of fairies available by Nyx.
Fairies ModNyx has also made mods for
Mermaids and
Zombies (apocalyptic, brain-eating ones).
For custom Magic sims there are 2 mods, I have both in game but have only tested the first one so far.
Become a Sorcerer by @Triplis (2x 10 level Dark/Light Skills and alignment; Mana gained by draining/sacrificing needs respectively)
The Art of Magic by WildWitch (Single 10 level Magecraft skill; Mana gained through meditation - Mana Bowl costs 5k) - She also has several other witchy things on that page like a scrying bowl etc.