Negate

Firebrand Archer

Whenever you cast a noncreature spell, this creature deals 1 damage to each opponent.

Aetherize

Return all attacking creatures to their owner's hand.

Niv-Mizzet, the Firemind

Flying
Whenever you draw a card, Niv-Mizzet, the Firemind deals 1 damage to any target.
{T}: Draw a card.

Razorkin Needlehead

Razorkin Needlehead has first strike during your turn.
Whenever an opponent draws a card, Razorkin Needlehead deals 1 damage to them.

Boltwave

Boltwave deals 3 damage to each opponent.

Lightning Bolt

Lightning Bolt deals 3 damage to any target.

Talisman of Creativity

{T}: Add {C}.
{T}: Add {U} or {R}. Talisman of Creativity deals 1 damage to you.

Case of the Ransacked Lab

Instant and sorcery spells you cast cost {1} less to cast.
To solve — You've cast four or more instant and sorcery spells this turn. (If unsolved, solve at the beginning of your end step.)
Solved — Whenever you cast an instant or sorcery spell, draw a card.

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Blasphemous Act

This spell costs {1} less to cast for each creature on the battlefield.
Blasphemous Act deals 13 damage to each creature.

Thought Vessel

You have no maximum hand size.
{T}: Add {C}.

Sol Ring

Flame Rift

Flame Rift deals 4 damage to each player.

Storm-Kiln Artist

Storm-Kiln Artist gets +1/+0 for each artifact you control.
Magecraft — Whenever you cast or copy an instant or sorcery spell, create a Treasure token.

Goblin Electromancer

Instant and sorcery spells you cast cost {1} less to cast.

Izzet Signet

Counterspell

Decanter of Endless Water

You have no maximum hand size.
{T}: Add one mana of any color.

Chaos Warp

The owner of target permanent shuffles it into their library, then reveals the top card of their library. If it's a permanent card, they put it onto the battlefield.

Kessig Flamebreather

Whenever you cast a noncreature spell, Kessig Flamebreather deals 1 damage to each opponent.

River Song's Diary

Imprint — Whenever a player casts an instant or sorcery spell from their hand, exile it instead of putting it into a graveyard as it resolves.
At the beginning of your upkeep, if there are four or more cards exiled with River Song's Diary, choose one of them at random. You may cast it without paying its mana cost.

Laboratory Maniac

If you would draw a card while your library has no cards in it, you win the game instead.

Fateful Showdown

Fateful Showdown deals damage to any target equal to the number of cards in your hand. Discard all the cards in your hand, then draw that many cards.

Niv-Mizzet, Parun

This spell can't be countered.
Flying
Whenever you draw a card, Niv-Mizzet, Parun deals 1 damage to any target.
Whenever a player casts an instant or sorcery spell, you draw a card.

Ruby Medallion

Red spells you cast cost {1} less to cast.

Niv-Mizzet, Visionary

Flying
You have no maximum hand size.
Whenever a source you control deals noncombat damage to an opponent, you draw that many cards.