Mobile Garrison is a common Artifact — Vehicle card from Aether Revolt (AER), collector number 165. Current market price: $0.30 (foil $1.64), TCGplayer market prices via Scryfall.
Whenever this Vehicle attacks, untap another target artifact or creature you control. Crew 2 (Tap any number of creatures you control with total power 2 or more: This Vehicle becomes an artifact creature until end of turn.)