Lethargy Trap 
Instant — Trap
If three or more creatures are attacking, you may pay rather than pay this spell's mana cost.
Attacking creatures get -3/-0 until end of turn.
Legality
standardNOT LEGALpioneerNOT LEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL