Teferi, Hero of Dominaria is the gold standard for control finishers
Sword Coast Sailor makes Karlach unblockable, and access to blue gives you a bunch of card draw and combat tricks to perform
Forth Eorlingas
This combo clears the entire board, then returns all of the Meditation player's permanents back to play
While there may be other powerful cards in Magic: the Gathering, Carnage Tyrant's unique combination of abilities makes it a strong choice for certain decks, particularly in a metagame where countermagic and targeted removal are prevalent
On the other hand, we played against Mono-Black Auras, which was overloaded with Dead Weights and Mire's Grasps, and it felt like we had zero chance of winning (in part because of the amount of removal our opponent had and in part because enchantments get around many of our sideboard cards, like Miscast and Seasoned Hallowblade)