Zealot's Conviction is a common Enchantment — Aura card from Phyrexia: All Will Be One (ONE), collector number 39. Current market price: $0.22 (foil $0.17), TCGplayer market prices via Scryfall.
Flash Enchant creature Enchanted creature gets +1/+1. Corrupted — As long as an opponent has three or more poison counters, enchanted creature gets an additional +1/+0 and has first strike.