Magus of the Chains is a rare Creature — Human Wizard card from Mystery Booster 2 (MB2), collector number 549. Current market price: $0.21, TCGplayer market prices via Scryfall.
If a player would draw a card except the first one they draw in each of their draw steps, that player discards a card instead. If the player discards a card this way, they draw a card. If the player doesn't discard a card this way, they mill a card.