Call for Unity is a rare Enchantment card from Aether Revolt (AER), collector number 9. Current market price: $0.20 (foil $0.73), TCGplayer market prices via Scryfall.
Revolt — At the beginning of your end step, if a permanent left the battlefield under your control this turn, put a unity counter on this enchantment. Creatures you control get +1/+1 for each unity counter on this enchantment.