Double Effectiveness

Casting this spell on another spellcaster within 30' (or on yourself), allows them to choose one aspect of any spell they cast on their next turn and double it. 

Range, damage, area of effect, # of targets. 

EX: Fireball - The range goes from 150' to 300' OR the AOE changes from 20' to 40' OR the damage goes from 8D6 to 16D6!

Another EX: Sleep - range 90' goes to 180' OR AOE goes from 20' to 40' OR # you can effect goes from 5D8 to 10D8.

If you are upcasting a spell, that is what you double. (2nd level sleep can effect 14D8)