Discard decks use effects that put cards from players' hands into their graveyards. Some attack opponents' resources directly, while others deliberately discard their own cards to fuel graveyard synergies or trigger additional abilities.
Tinybones, Trinket Thief rewards stripping cards from opposing hands, while Bone Miser converts your own discards into mana, cards, and creatures. Archfiend of Ifnir turns cycling or discarding into -1/-1 counters for opposing creatures.