Plain and simple, sometimes things gotta die. Like in any game, offensive and defensive positions are constantly shifting. This is especially true in multiplayer games. Threats are cards capable of shifting a player into an aggressive position. Answers help to restore parity or initiate counter-offensives. Single-Target Removal attempts to answer opposing threats on a card-to-card basis, often for much less mana than the threat cost.
Most removal players consider is characterized by costing much less than whatever the threat was. If I can answer a 5-mana threat with a 1-mana answer, then my answer is considered efficient. Typically speaking, however, mana efficiency comes at the expense of usability. As a result, efficient removal is sometimes limited in what threats it answers or how permanently it answers threats.
Exile
Exile-based removal is strong because it prevents graveyard synergies from functioning. Instead of going to the graveyard, the removed card is rendered inaccessible for all but a few niche strategies. Swords to Plowshares, Path to Exile, and Vraska’s Contempt are all spells that exile permanents.
Destruction
Destruction-based removal is strong because it’s available in a variety of colors. Every color has some way to destroy permanents, albeit with a variety of drawbacks. The biggest issue is the amount of abilities that enable permanents to survive destruction. Still, Doom Blade is considered a gold standard of removal.
Bounce
Bounce spells are my favorite kind of removal; I am Unsummoned Skull, after all! With bounce spells, you return a creature an opponent controls to their hand, so they still have access to the card and don’t feel as bad about losing it. It does mean that they don’t get to play it when they want to, and all of their setup needs to be redone. Cards like Unsummon can even be used to protect your own threats in a pinch!