Memory Casting

You gain the ability to cast one unprepared spell without using a spell slot once per long rest.

After this ability is used until a long rest, for any spell casted by you, roll a d20.  If the d20 is a 1,2,10,19, or 20, the spell casted will be a random spell from your spellbook. 

The dm will roll a die equal to the amount of spells within the spellbook, according to the table below, rounded down to the nearest spell to determine which spell will be casted.

Areas/targets chosen for A.O.E spells are chosen by the dm.  For spells that target multiple chosen targets, the first shot of the salvo is chosen by the dm.