Breaking Point

Any player may have Breaking Point deal 6 damage to them. If no one does, destroy all creatures. Creatures destroyed this way can't be regenerated.

Howlpack Avenger

Whenever a permanent you control is dealt damage, Howlpack Avenger deals that much damage to any target.
{1}{R}: Howlpack Avenger gets +2/+0 until end of turn.
Nightbound (If a player casts at least two spells during their own turn, it becomes day next turn.)

Ill-Tempered Loner

Whenever Ill-Tempered Loner is dealt damage, it deals that much damage to any target.
{1}{R}: Ill-Tempered Loner gets +2/+0 until end of turn.
Daybound (If a player casts no spells during their own turn, it becomes night next turn.)

Ill-Tempered Loner // Howlpack Avenger

Injury

Aftermath (Cast this spell only from your graveyard. Then exile it.)
Injury deals 2 damage to target creature and 2 damage to target player or planeswalker.

Insult

Damage can't be prevented this turn. If a source you control would deal damage this turn, it deals double that damage instead.

Insult // Injury

Skewer the Critics

Spectacle {R} (You may cast this spell for its spectacle cost rather than its mana cost if an opponent lost life this turn.)
Skewer the Critics deals 3 damage to any target.

Blood Oath

Choose a card type. Target opponent reveals their hand. Blood Oath deals 3 damage to that player for each card of the chosen type revealed this way. (Artifact, battle, creature, enchantment, instant, kindred, land, planeswalker, and sorcery are card types.)

Screaming Nemesis

Haste
Whenever Screaming Nemesis is dealt damage, it deals that much damage to any other target. If a player is dealt damage this way, they can't gain life for the rest of the game.

Pariah's Shield

All damage that would be dealt to you is dealt to equipped creature instead.
Equip {3}

Vexing Devil

When Vexing Devil enters, any opponent may have it deal 4 damage to them. If a player does, sacrifice Vexing Devil.

Stuffy Doll

Indestructible
As Stuffy Doll enters, choose a player.
Whenever Stuffy Doll is dealt damage, it deals that much damage to the chosen player.
{T}: Stuffy Doll deals 1 damage to itself.

Browbeat

Any player may have Browbeat deal 5 damage to them. If no one does, target player draws three cards.

Mountain

Vexing Arcanix

{3}, {T}: Target player chooses a card name, then reveals the top card of their library. If that card has the chosen name, that player puts it into their hand. Otherwise, they put it into their graveyard and Vexing Arcanix deals 2 damage to them.

Jester's Mask

Jester's Mask enters tapped.
{1}, {T}, Sacrifice Jester's Mask: Target opponent puts the cards from their hand on top of their library. Search that player's library for that many cards. That player puts those cards into their hand, then shuffles.

Mages' Contest

You and target spell's controller bid life. You start the bidding with a bid of 1. In turn order, each player may top the high bid. The bidding ends if the high bid stands. The high bidder loses life equal to the high bid. If you win the bidding, counter that spell.

Sorrow's Path

{T}: Choose two target blocking creatures controlled by the same opponent. If each of those creatures could block all creatures that the other is blocking, remove both of them from combat. Each one then blocks all creatures the other was blocking.
Whenever Sorrow's Path becomes tapped, it deals 2 damage to you and each creature you control.

Pyroclasm

Pyroclasm deals 2 damage to each creature.

Glasses of Urza

Provoke the Trolls

Provoke the Trolls deals 3 damage to any target. If a creature is dealt damage this way, it gets +5/+0 until end of turn.

Blasphemous Act

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

Mogg Maniac

Whenever Mogg Maniac is dealt damage, it deals that much damage to target opponent or planeswalker.

Risk Factor

Target opponent may have Risk Factor deal 4 damage to them. If that player doesn't, you draw three cards.
Jump-start (You may cast this card from your graveyard by discarding a card in addition to paying its other costs. Then exile this card.)

Brash Taunter

Indestructible
Whenever Brash Taunter is dealt damage, it deals that much damage to target opponent.
{2}{R}, {T}: Brash Taunter fights another target creature.