Esmeralda, the Significant

Haste, Vigilance, Trample

Whenever Esmeralda, the Significant attacks, target creature defending player controls gets
-X/-X until end of turn, where X is Esmeralda's power. Double Esmeralda's power and toughness until end of turn. Sacrifice Esmeralda at the end of the turn, if you don't sacrifice another creature instead.