Tactics
Aside from his poisoning wand Loki might seem like another apprentice, but as soon as you level up you realize that he only gets one perk to choose from upon leveling up. Bookworm might help but the chances of it appearing is lower than it already is for every other character.
Notes
You don't need to win 20 games to unlock this character you just need to play 20. Cheap way to unlock him is to just die 20 times.
It used to take 200 games to unlock this character!