Phantasmal Sphere
{1}{U}Creature — Illusion
Flying At the beginning of your upkeep, put a +1/+1 counter on this creature, then sacrifice this creature unless you pay {1} for each +1/+1 counter on it. When this creature leaves the battlefield, target opponent creates an X/X blue Orb creature token with flying, where X is the number of +1/+1 counters on this creature.