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Tinybones, Bauble Burglar

Whenever an opponent discards a card, exile it from their graveyard with a stash counter on it.
During your turn, you may play cards you don't own with stash counters on them from exile, and mana of any type can be spent to cast those spells.
{3}{B}, {T}: Each opponent discards a card. Activate only as a sorcery.

Painful Quandary

Whenever an opponent casts a spell, that player loses 5 life unless they discard a card.

Seeker's Folly

Choose one —
• Target opponent discards two cards.
• Creatures your opponents control get -1/-1 until end of turn.

Necrogen Mists

At the beginning of each player's upkeep, that player discards a card.

Syphon Mind

Each other player discards a card. You draw a card for each card discarded this way.