Some tabletop games lack narratives or worldbuilding, choosing instead to forefront gameplay and mechanics. However, this isn't a universal case. Some board or card games build a fictional universe to accompany the gameplay. This is much more common in wargames and tabletop roleplaying games, both of which typically include heavy narrative emphasis. And with any sufficiently epic storyline comes a suitably epic villain.
Many tabletop antagonists are responsible for countless wicked, evil acts that span across many different storylines. The best tabletop villains have countless minions for players to either play as or against, and may even be an active presence in the game themselves.
10 Nyarlathotep
Call Of Cthulhu
Many of Call of Cthulhu's most iconic villains are drawn directly from H. P. Lovecraft's writing or the writing of authors inspired by him. However, the RPG expands on their nature and history in a way that sheds fresh light on them. Through Lovecraft's writing and Call of Cthulhu's worldbuilding, Nyarlathotep has become one of the game's most infamous antagonists.
Nyarlathotep is a deceiver and corrupter who delights in ruining his victims. His preferred methods of villainy include granting wishes in the most horrific, life-destroying ways possible and driving those around him to mass murder and sacrifice. Nyarlathotep takes a more grounded, mundane joy from his acts than many of Call of Cthulhu's more incomprehensible villains, adding a twist of personal cruelty to his villainy.
9 Nicol Bolas
Magic: The Gathering
Nicol Bolas is one of Magic: The Gathering's oldest and most powerful Planeswalkers. In stories set before the Mending, he is a vicious god who creates entire planes and civilizations only to hunt them to extinction for fun. Following the Mending, he became Magic: The Gathering's most recurring villain as he wove complex plans to regain his lost power.
Nicol Bolas is responsible for countless deaths and many planes' devastations. His worst act was stranding Planeswalkers on Ravnica and forcing Liliana Vess to lead an army of Eternals to butcher everyone. Unlike Magic's other villains like the warped Eldrazi and the misguidedly benevolent New Phyrexians, Nicol Bolas is well aware of that his actions are evil. He simply doesn't care.
8 Mnggal-Mnggal
Star Wars d20
The Star Wars d20 roleplaying system shares many villains with the Star Wars movies and Expanded Universe. However, it also invents some of its own for players to go up against. Mnggal-Mnggal is an entity dominating large sections of the Star Wars galaxy by corrupting existing beings and treating them like appendages to spread its presence.
Mnggal-Mnggal is something between a sapient creature and a plague that spreads through thick gray ooze. This substance agonizingly warps the victim until they're a hollow husk with no free will. However, Mnggal-Mnggal is sapient and seems to enjoy this pain and corruption, making it one of the Star Wars galaxy's most heinous beings.
7 Them
Ten Candles
Ten Candles is a one-shot RPG that focuses on survival and secrets in a dark world. Ten Candles' player characters are the few survivors of their local area after the arrival of creatures known only as Them. Due to Ten Candles' heavily improvisational nature, with heavy player input, the nature of Them changes with every game.
However, Them have a few things in common in every game of Ten Candles. They are always responsible for the world's devastation, they are always weakened by light, and they are responsible for turning the world dark. As a result, there are few iterations of Ten Candles where they are anything short of monstrous.
6 Tharizdun
Dungeons & Dragons
Dungeons & Dragons has plenty of mortal villains and many evil gods. However, none of its villains come close to Tharizdun's misanthropy and corruption. Tharizdun is a god driven to evil and irrationality thanks to his exposure to a shard of pure evil. He is responsible for the creation of the Abyss and hungers to destroy the cosmos.
Tharizdun is responsible for some of Dungeons & Dragons' greatest depravities due to helping create the Abyss. Anything that demons are able to do, including the cosmos-spanning Blood War, are because of his actions. Tharizdun is so malevolent that D&D's good and evil gods formed an alliance to imprison him and protect reality.
5 True Fae
Changeling: The Lost
True Fae are the overarching antagonists of the Chronicles of Darkness gameline Changeling: The Lost. They are the only reason there are Changelings to begin with. The True Fae operate by kidnapping people from Earth, including children, and forcibly warping them into servants.
The True Fae are almost entirely solipsistic, caring nothing for other creatures that aren't themselves. Changeling: The Lost is a game about overcoming trauma due to how sheerly horrific being captured by the True Fae is. Any of the potential reasons for their actions, including reproduction, their continued existence, or sheer cruelty, simply paint them as monsters.
4 Omega
Mutants & Masterminds
Much of Mutants & Masterminds focuses on low-level street crime or more conventional global threats. But Omega is a villain most relevant to the very highest reaches of Mutants & Masterminds' worldbuilding. He isn't just a threat to individual universes but to the multiverse in its entirety.
Omega is a fallen hero who once helped fight against entropy. However, he has since surrendered to the idea that every universe will be destroyed. Omega prefers to corrupt Mutants & Masterminds' greatest heroes into his own allies before annihilating entire universes to add to his power.
3 The Drukhari
Warhammer 40,000
The Warhammer 40,000 universe is one of the bleakest in gaming history, so much so that it gave rise to the term "grimdark." Every one of the factions fighting over the galaxy has some deep flaws, with even the alleged protagonists in the Imperium of Man being vicious fascists. However, few villains are more unpleasant than the Drukhari, also known as Dark Eldar.
The Drukhari are slavers and pirates who strike across the universe. Their main goal is to capture prisoners, who are then put to work, tortured, experimented on, or simply used for their amusement. The Drukhari actually need to inflict suffering to keep existing. However, Warhammer 40,000 shows that Aeldari can live in other ways. As a result, they choose to be as cruel as possible just for their own satisfaction.
2 Stefan Amaris
BattleTech
BattleTech usually runs on grey morality, with sympathetic factions and characters having their dark side, and most antagonists having depth and light points. However, Stefan Amaris is as close to an overarching antagonist as BattleTech gets and is responsible for the current awful state of the universe.
Amaris spent decades of his life maneuvering BattleTech's various factions into position to start a galaxy-spanning war. His history is a long list of betrayals, murders, and atrocities. Some of his worst actions include nuking his own planets during his forces' retreat to Terra, just to slow their pursuers down.
1 Charon The Boatman
Pathfinder
Pathfinder's daemons don't seek to control everything like devils or to corrupt everything like demons. They simply seek to destroy all life in Pathfinder's cosmos. Charon the Boatman is the overall ruler of the daemons as the Horseman of Death. Although he's every bit as hateful and misanthropic as his fellows, Charon's sheer wickedness sets him a cut above.
Charon is more controlled and subtle than the typical daemon. He likes to bargain with the desperate and pretend to assist them, only to plan their inevitable death and collect their souls for himself. He has committed numerous atrocities, including aging an entire civilization into dust. Even other unmatched evils in Pathfinder, such as Asmodeus, loathe Charon for his cruelty.