Niv-Mizzet, the Firemind

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

Ragefire Hellkite

Flying
Whenever Ragefire Hellkite attacks, you may sacrifice another creature. If you do, Ragefire Hellkite gains double strike until end of turn.

Shivan Dragon

Flying
{R}: This creature gets +1/+0 until end of turn.

Stifle

Counter target activated or triggered ability. (Mana abilities can't be targeted.)

Izzet Charm

Choose one —
• Counter target noncreature spell unless its controller pays {2}.
• Izzet Charm deals 2 damage to target creature.
• Draw two cards, then discard two cards.

Ionize

Counter target spell. Ionize deals 2 damage to that spell's controller.

Ryusei, the Falling Star

Flying
When Ryusei, the Falling Star dies, it deals 5 damage to each creature without flying.

Double Negative

Teferi's Veil

Whenever a creature you control attacks, it phases out at end of combat. (While it's phased out, it's treated as though it doesn't exist. It phases in before you untap during your next untap step.)

Gelectrode

{T}: Gelectrode deals 1 damage to any target.
Whenever you cast an instant or sorcery spell, you may untap Gelectrode.

Electrolyze

Electrolyze deals 2 damage divided as you choose among one or two targets.
Draw a card.

Volcanic Island

Highland Lake

Highland Lake enters tapped.
{T}: Add {U} or {R}.

Sneak Attack

{R}: You may put a creature card from your hand onto the battlefield. That creature gains haste. Sacrifice the creature at the beginning of the next end step.

Crimson Hellkite

Flying
{X}, {T}: Crimson Hellkite deals X damage to target creature. Spend only red mana on X.

Steam Vents

({T}: Add {U} or {R}.)
As Steam Vents enters, you may pay 2 life. If you don't, it enters tapped.

Vampiric Dragon

Flying
Whenever a creature dealt damage by Vampiric Dragon this turn dies, put a +1/+1 counter on Vampiric Dragon.
{1}{R}: Vampiric Dragon deals 1 damage to target creature.

Mox Diamond

If Mox Diamond would enter, you may discard a land card instead. If you do, put Mox Diamond onto the battlefield. If you don't, put it into its owner's graveyard.
{T}: Add one mana of any color.

Siege Dragon

Flying
When Siege Dragon enters, destroy all Walls your opponents control.
Whenever Siege Dragon attacks, if defending player controls no Walls, it deals 2 damage to each creature without flying that player controls.

Dracoplasm

Flying
As Dracoplasm enters, sacrifice any number of creatures. Dracoplasm's power becomes the total power of those creatures and its toughness becomes their total toughness.
{R}: Dracoplasm gets +1/+0 until end of turn.

Dack's Duplicate

You may have Dack's Duplicate enter as a copy of any creature on the battlefield, except it has haste and dethrone. (Whenever it attacks the player with the most life or tied for most life, put a +1/+1 counter on it.)

Impulse

Look at the top four cards of your library. Put one of them into your hand and the rest on the bottom of your library in any order.

Suffocating Blast

Counter target spell and Suffocating Blast deals 3 damage to target creature.

Gifts Ungiven

Search your library for up to four cards with different names and reveal them. Target opponent chooses two of those cards. Put the chosen cards into your graveyard and the rest into your hand. Then shuffle.

Archwing Dragon

Flying, haste
At the beginning of the end step, return Archwing Dragon to its owner's hand.

Shivan Reef

{T}: Add {C}.
{T}: Add {U} or {R}. Shivan Reef deals 1 damage to you.

Wee Dragonauts

Flying
Whenever you cast an instant or sorcery spell, Wee Dragonauts gets +2/+0 until end of turn.

Hypersonic Dragon

Flying, haste
You may cast sorcery spells as though they had flash. (You may cast them any time you could cast an instant.)

Counterflux

This spell can't be countered.
Counter target spell you don't control.
Overload {1}{U}{U}{R} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

Curiosity

Enchant creature
Whenever enchanted creature deals damage to an opponent, you may draw a card.