Unstable Shield

An crackling barrier of unstable force appears and protects you. Until the start of your next turn, you have a +5 bonus to AC, including against the triggering attack.

When an attack misses you while your Unstable Shield spell is active, the attacker is immediately hit with a single Magic Missile bolt, which deals 3 (1d4+1) force damage. If you are hit by the Magic Missile spell, you take no damage from it and reflect double the amount of bolts back at the caster.

If a Magic Missile bolt would bounce between two Unstable Shields indefinitely, both shields overload and send out an uncontrollable explosion of Magic Missile bolts. Each creature within 30 feet of either caster (not including themselves - but they can be hit by the other explosion) are hit by 2 (1d4) Magic Missile bolts, each dealing 3 (1d4+1) force damage. Both Unstable Shields are then removed.

At Higher Levels: If you cast this spell using a spell slot of 3rd level or higher, the number of bolts reflected at attackers is increased by one per spell level above second, and the number of bolts reflected if it overloads increases by 1d4.