Twenty Lessons 
Sorcery
Cast a random Lesson spell without paying its mana cost. If that spell has X in its mana cost, X is 3. (As of today, there are 20 lessons. Perhaps look up a list and roll a d20?)
Legality
standardNOT LEGALpioneerNOT LEGALmodernNOT LEGALlegacyNOT LEGALvintageNOT LEGALcommanderNOT LEGAL