MTG Keyword Rules — Comprehensive Rules Glossary

Madness is a keyword that represents two abilities. The first is a static ability that functions while the card with madness is in a player’s hand. The second is a triggered ability that functions when the first ability is applied. “Madness [cost]” means “If a player would discard this card, that player discards it, but exiles it instead of putting it into their graveyard” and “When this card is exiled this way, its owner may cast it by paying [cost] rather than paying its mana cost. If that player doesn’t, they put this card into their graveyard.”

Casting a spell using its madness ability follows the rules for paying alternative costs in rules 601.2b and 601.2f–h.

After resolving a madness triggered ability, if the exiled card wasn’t cast and was moved to a public zone, effects referencing the discarded card can find that card. See rule 400.7k.