Osseous Exhale 
Instant
As an additional cost to cast this spell, you may behold a Dragon. (You may choose a Dragon you control or reveal a Dragon card from your hand.) Osseous Exhale deals 5 damage to target attacking or blocking creature. If a Dragon was beheld, you gain 2 life.
Legality
standardLEGALpioneerLEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL