Spot Removal

Spot removal destroys, exiles, or otherwise deals with a single threat. In a four-player game, threats come from every direction. You need efficient answers or you'll fall behind.

Run 8-12 targeted removal spells. Instant-speed is better than sorcery-speed because you can respond to threats as they happen rather than waiting for your turn.

By permanent type

Creature removal:

Swords to Plowshares — 1 mana, exile. The opponent gains life, but exile is worth it. White staple.
Path to Exile — 1 mana, exile. The opponent gets a land. Slightly worse than Swords but still excellent.
Go for the Throat — 2 mana, destroys nonartifact creatures. Black staple.
Chaos Warp — 3 mana, shuffles any permanent into its owner's library. They reveal the top card and it might be worse. Red's only clean answer to enchantments.

Artifact / Enchantment removal:

Nature's Claim — 1 mana, destroys an artifact or enchantment. Opponent gains 4 life. Efficient.
Krosan Grip — 3 mana, split second (can't be responded to). Kills an artifact or enchantment with no counterplay.
Vandalblast — 1 mana to hit one artifact, or overload for 5 to hit all opponents' artifacts.

Flexible removal (any permanent):

Generous Gift — 3 mana, destroys any permanent. Opponent gets a 3/3 elephant. White.
Beast Within — 3 mana, destroys any permanent. Opponent gets a 3/3 beast. Green.
Anguished Unmaking — 3 mana, exiles any nonland permanent. You lose 3 life. Orzhov (B/W).
Assassin's Trophy — 2 mana, destroys any permanent. Opponent gets a basic land. Golgari (B/G).

Flexible removal costs a premium (usually 3 mana, or 2 with a downside). It's worth it because you're never stuck with a dead card. Beast Within answers a creature, an enchantment, a planeswalker, or a problematic land.

Counterspells

Blue's primary form of interaction. They stop spells before they resolve.

Counterspell — 2 mana, counters anything. The baseline.
Swan Song — 1 mana, counters instants, sorceries, or enchantments. Opponent gets a 2/2 bird.
Negate — 2 mana, counters noncreature spells. Hits most of the dangerous stuff.
Fierce Guardianship — free if your commander is on the battlefield. Counters noncreature spells.
Mana Drain — 2 mana, counters anything and gives you the mana cost as colorless next turn. Expensive card to buy, ridiculous when you have it.

Counterspells double as protection for your own important plays. Cast your combo piece, hold up Swan Song to protect it.

Removal by color

White: Exile-based creature removal (Swords, Path), flexible permanent destruction (Generous Gift), enchantment removal.

Blue: Counterspells and bounce (Cyclonic Rift, Chain of Vapor). Blue doesn't destroy things on the battlefield easily but prevents them from landing.

Black: Creature destruction (Go for the Throat, Deadly Rollick, Infernal Grasp) and -X/-X effects (Toxic Deluge, which is technically a board wipe).

Red: Damage-based removal (hits smaller creatures), artifact destruction (Vandalblast, Abrade, By Force). Chaos Warp for everything else.

Green: Artifact and enchantment removal (Nature's Claim, Krosan Grip), fight effects for creatures (Ram Through, Tail Swipe), and Beast Within for flexibility.

Efficiency matters

A 1-mana removal spell is significantly better than a 4-mana one. You're more likely to have 1 mana open and still be developing your board. The best removal in the format costs 1-2 mana.

At 3 mana, removal needs to be flexible (Beast Within, Anguished Unmaking) or provide extra value to justify the cost. At 4+, it should be doing something beyond just removing one thing (Ravenous Chupacabra gives you a body, Curtains' Call costs less with spectacle).