Training Grounds is a rare Enchantment card from March of the Machine: The Aftermath Promos (PMAT), collector number 9p. Current market price: $9.30 (foil $13.61), TCGplayer market prices via Scryfall.
Activated abilities of creatures you control cost {2} less to activate. This effect can't reduce the mana in that cost to less than one mana.
All March of the Machine: The Aftermath Promos cards and prices