Mystic Might is a rare Enchantment — Aura card from Ice Age (ICE), collector number 86. Current market price: $0.53, TCGplayer market prices via Scryfall.
Enchant land you control Cumulative upkeep {1}{U} (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.) Enchanted land has "{T}: Target creature gets +2/+2 until end of turn."