What it does
Mayhem lets you cast a card from your graveyard for its mayhem cost, but only if it was put there from your hand this turn—typically through discarding. It's a newer ability tied to "discard matters" strategies, letting you turn a discarded card into immediate value instead of losing it entirely.
The key nuance: the card has to have been discarded (or otherwise put into your graveyard from hand) that same turn. You can't dig up a card that's been sitting in your graveyard since an earlier turn. Also, like flashback, a card cast with mayhem is exiled if it would leave the stack, so it won't end up back in your graveyard for reuse.
In Commander, mayhem rewards rummaging, looting, and discard outlets—you sculpt your hand and still cash in the "thrown away" cards, generating card advantage from what looks like card disadvantage.











