Ionize

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

Replicate

Create a token that's a copy of target creature you control.

Repudiate

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

Repudiate // Replicate

Countersquall

Counter target noncreature spell. Its controller loses 2 life.

Undermine

Counter target spell. Its controller loses 3 life.

Niv-Mizzet Reborn

Flying
When Niv-Mizzet Reborn enters, reveal the top ten cards of your library. For each color pair, choose a card that's exactly those colors from among them. Put the chosen cards into your hand and the rest on the bottom of your library in a random order.

Render Silent

Counter target spell. Its controller can't cast spells this turn.

Voidslime

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

Dovin's Veto

This spell can't be countered.
Counter target noncreature spell.

Perplex

Counter target spell unless its controller discards their hand.
Transmute {1}{U}{B} ({1}{U}{B}, Discard this card: Search your library for a card with the same mana value as this card, reveal it, put it into your hand, then shuffle. Transmute only as a sorcery.)

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.")

Absorb

Suffocating Blast

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

Mindswipe

Counter target spell unless its controller pays {X}. Mindswipe deals X damage to that spell's controller.

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.

Double Negative

Drown in the Loch

Choose one —
• Counter target spell with mana value less than or equal to the number of cards in its controller's graveyard.
• Destroy target creature with mana value less than or equal to the number of cards in its controller's graveyard.

Plasm Capture

Counter target spell. At the beginning of your next first main phase, add X mana in any combination of colors, where X is that spell's mana value.

Overrule

Counter target spell unless its controller pays {X}. You gain X life.

Reinterpret

Counter target spell. You may cast a spell with equal or lesser mana value from your hand without paying its mana cost.

Hindering Light

Counter target spell that targets you or a permanent you control.
Draw a card.

Decisive Denial

Choose one —
• Target creature you control fights target creature you don't control. (Each deals damage equal to its power to the other.)
• Counter target noncreature spell unless its controller pays {3}.