Mounted Railcannon

Equipped creature has defender and "{1},{t}: This
creature deals 1 damage to target creature" and
"When this creature crews a Vehicle, when that Vehicle attacks it deals 3 damage to target
permanent defending player controls, then
unattach Mounted Railcannon."
Equip {3} ({3}: Attatch to target creature you control.
Equip only as a sorcery.)