Ball Lightning (MB2 130)

Creature — Elemental • Mana cost: {R}{R}{R} • Mystery Booster 2 • Rare

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
Haste (This creature can attack and {T} as soon as it comes under your control.)
At the beginning of the end step, sacrifice this creature.

Illustrated by Dave Dorman.