Case of the Gateway Express 
Enchantment — Case
When this Case enters, choose target creature you don't control. Each creature you control deals 1 damage to that creature. To solve — Three or more creatures attacked this turn. (If unsolved, solve at the beginning of your end step.) Solved — Creatures you control get +1/+0.
Legality
standardLEGALpioneerLEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL