See Red 

Enchantment — Aura
Enchant creature Enchanted creature gets +2/+1 and has first strike. At the beginning of your end step, if you didn't attack with a creature this turn, sacrifice this Aura.
Legality
standardNOT LEGALpioneerLEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL