Aeromoeba

Flying
Discard a card: Switch this creature's power and toughness until end of turn.

Oblivion Crown

Flash (You may cast this spell any time you could cast an instant.)
Enchant creature
Enchanted creature has "Discard a card: This creature gets +1/+1 until end of turn."

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Anvil of Bogardan

Players have no maximum hand size.
At the beginning of each player's draw step, that player draws an additional card, then discards a card.

Green Goblin

Flying, menace
Spells you cast from your graveyard cost {2} less to cast.
Goblin Formula — Each nonland card in your graveyard has mayhem. The mayhem cost is equal to its mana cost. (You may cast a card from your graveyard for its mayhem cost if you discarded it this turn. Timing rules still apply.)

Norman Osborn

Norman Osborn can't be blocked.
Whenever Norman Osborn deals combat damage to a player, he connives. (Draw a card, then discard a card. If you discarded a nonland card, put a +1/+1 counter on this creature.)
{1}{U}{B}{R}: Transform Norman Osborn. Activate only as a sorcery.

Norman Osborn // Green Goblin

Aquamoeba

Discard a card: Switch this creature's power and toughness until end of turn.

Island

Soul Ransom

Enchant creature
You control enchanted creature.
Discard two cards: This Aura's controller sacrifices it, then draws two cards. Only your opponents may activate this ability.