Brineborn Cutthroat

Flash (You may cast this spell any time you could cast an instant.)
Whenever you cast a spell during an opponent's turn, put a +1/+1 counter on Brineborn Cutthroat.

Acidic Slime

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
When Acidic Slime enters the battlefield, destroy target artifact, enchantment, or land.

Rattleclaw Mystic

{T}: Add {G}, {U}, or {R}.
Morph {2} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)
When Rattleclaw Mystic is turned face up, add {G}{U}{R}.

Baral, Chief of Compliance

Instant and sorcery spells you cast cost {1} less to cast.
Whenever a spell or ability you control counters a spell, you may draw a card. If you do, discard a card.

Biovisionary

At the beginning of the end step, if you control four or more creatures named Biovisionary, you win the game.

Exclude

Counter target creature spell.
Draw a card.

Insidious Will

Choose one —
• Counter target spell.
• You may choose new targets for target spell.
• Copy target instant or sorcery spell. You may choose new targets for the copy.

Reclamation Sage

When Reclamation Sage enters the battlefield, you may destroy target artifact or enchantment.

Terastodon

When Terastodon enters the battlefield, you may destroy up to three target noncreature permanents. For each permanent put into a graveyard this way, its controller creates a 3/3 green Elephant creature token.

Thoughtcast

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
Draw two cards.

Explosive Vegetation

Search your library for up to two basic land cards, put them onto the battlefield tapped, then shuffle.

Rampant Growth

Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Shock

Coiling Oracle

When Coiling Oracle enters the battlefield, reveal the top card of your library. If it's a land card, put it onto the battlefield. Otherwise, put that card into your hand.

Altered Ego

This spell can't be countered.
You may have Altered Ego enter the battlefield as a copy of any creature on the battlefield, except it enters with X additional +1/+1 counters on it.

Goblin Electromancer

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

Blustersquall

Tap target creature you don't control.
Overload {3}{U} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

Larger Than Life

Target creature gets +4/+4 and gains trample until end of turn.

Archaeomancer

When Archaeomancer enters the battlefield, return target instant or sorcery card from your graveyard to your hand.

Heartfire

As an additional cost to cast this spell, sacrifice a creature or planeswalker.
Heartfire deals 4 damage to any target.

Body Double

You may have Body Double enter the battlefield as a copy of any creature card in a graveyard.

Arcane Melee

Instant and sorcery spells cost {2} less to cast.

Clone

You may have Clone enter the battlefield as a copy of any creature on the battlefield.

Vizier of Many Faces

You may have Vizier of Many Faces enter the battlefield as a copy of any creature on the battlefield, except if Vizier of Many Faces was embalmed, the token has no mana cost, it's white, and it's a Zombie in addition to its other types.
Embalm {3}{U}{U}

Prophetic Bolt

Prophetic Bolt deals 4 damage to any target. Look at the top four cards of your library. Put one of those cards into your hand and the rest on the bottom of your library in any order.

Cancel

Spell Pierce

Counter target noncreature spell unless its controller pays {2}.

Pyre Hound

Trample
Whenever you cast an instant or sorcery spell, put a +1/+1 counter on Pyre Hound.

Riku of Two Reflections

Whenever you cast an instant or sorcery spell, you may pay {U}{R}. If you do, copy that spell. You may choose new targets for the copy.
Whenever another nontoken creature enters the battlefield under your control, you may pay {G}{U}. If you do, create a token that's a copy of that creature.

Colossal Might

Target creature gets +4/+2 and gains trample until end of turn.

Scale Up

Until end of turn, target creature you control becomes a green Wurm with base power and toughness 6/4.
Overload {4}{G}{G} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

Dual Casting

Enchant creature
Enchanted creature has "{R}, {T}: Copy target instant or sorcery spell you control. You may choose new targets for the copy."