Wild Magic Cantrip

You have a wild and unstable magic infused into your veins by Auntie Mirre and her 'sisters'.
This magic is new and unknown to you.
Each time you attempt to cast a cantrip, roll a D100 to see what kind of magic you cast.
Only when you (accidentally) cast the same cantrip twice, you can remember how to cast it and add it to your spell-list.