Strong Back is a rare Enchantment — Aura card from Fallout (PIP), collector number 83. Current market price: $1.63 (foil $3.22), TCGplayer market prices via Scryfall.
Enchant creature Equip abilities you activate that target enchanted creature cost {3} less to activate. Aura spells you cast that target enchanted creature cost {3} less to cast. Enchanted creature gets +2/+2 for each Aura and Equipment attached to it.