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.)

Countersquall

Counter target noncreature spell. Its controller loses 2 life.

Summoner's Bane

Counter target creature spell. Create a 2/2 blue Illusion creature token.

Undermine

Counter target spell. Its controller loses 3 life.

Lightning Shrieker

Flying, trample, haste
At the beginning of the end step, this creature's owner shuffles it into their library.

Geist Snatch

Counter target creature spell. Create a 1/1 blue Spirit creature token with flying.

Mystic Genesis

Counter target spell. Create an X/X green Ooze creature token, where X is that spell's mana value.

Absorb

Punish Ignorance

Counter target spell. Its controller loses 3 life and you gain 3 life.

Mindswipe

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

Launch Mishap

Counter target creature or planeswalker spell. Create a 1/1 colorless Thopter artifact creature token with flying.

Ana Battlemage

Kicker {2}{U} and/or {1}{B} (You may pay an additional {2}{U} and/or {1}{B} as you cast this spell.)
When this creature enters, if it was kicked with its {2}{U} kicker, target player discards three cards.
When this creature enters, if it was kicked with its {1}{B} kicker, tap target untapped creature and that creature deals damage equal to its power to its controller.

Voracious Greatshark

Flash (You may cast this spell any time you could cast an instant.)
When this creature enters, counter target artifact or creature spell.

Render Silent

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

Blitz Hellion

Trample, haste
At the beginning of the end step, this creature's owner shuffles it into their library.

Bar the Gate

Counter target creature or planeswalker spell. Venture into the dungeon. (Enter the first room or advance to the next room.)

Ionize

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

Psionic Pulse

Counter target noncreature spell. (Then exile this card. You may cast the creature later from exile.)

Sapphire Dragon

Flying
Whenever this creature attacks or blocks, scry 2.

Sapphire Dragon // Psionic Pulse

Essence Backlash

Counter target creature spell. Essence Backlash deals damage equal to that spell's power to its controller.

Access Denied

Counter target spell. Create X 1/1 colorless Thopter artifact creature tokens with flying, where X is that spell's mana value.

Psychic Barrier

Counter target creature spell. Its controller loses 1 life.

Molten Influence

Counter target instant or sorcery spell unless its controller has Molten Influence deal 4 damage to them.

Frilled Mystic

Flash
When this creature enters, you may counter target spell.

Mystic Snake

Flash
When this creature enters, counter target spell.

Dismal Failure

Counter target spell. Its controller discards a card.

Hedron-Field Purists

Level up {2}{W} ({2}{W}: Put a level counter on this. Level up only as a sorcery.)
LEVEL 1-4
1/4
If a source would deal damage to you or a creature you control, prevent 1 of that damage.
LEVEL 5+
2/5
If a source would deal damage to you or a creature you control, prevent 2 of that damage.

Lullmage Mentor

Whenever a spell or ability you control counters a spell, you may create a 1/1 blue Merfolk creature token.
Tap seven untapped Merfolk you control: Counter target spell.

Dash Hopes

When you cast this spell, any player may pay 5 life. If a player does, counter Dash Hopes.
Counter target spell.

Mesmeric Glare

Counter target spell with mana value 3 or less. (Then exile this card. You may cast the creature later from exile.)

Hypnotic Sprite

Hypnotic Sprite // Mesmeric Glare

Deny the Witch

Counter target spell, activated ability, or triggered ability. Its controller loses life equal to the number of creatures you control.