- BattleTech: Just about all the Successor States were quite happy to blow each other to kingdom come. And then the Clans came, and all of a sudden, Arch Enemies were forming alliances to stop the threat. A few decades later, the Word of Blake started nuking everyone. So the Successor States ended up forming an alliance with the Clans to nuke the Blakists back.
- World of Darkness:
- Beast: The Primordial: Heroes will happily team up with any other race in the New World of Darkness for the sake of hunting down and killing Beasts. This is intended to show just why they are Designated Heroes; they are so obsessive that they will gladly ally with actually evil monsters to kill a harmless Beast, simply because they are so fixated on killing Beasts that they regard other supernatural entities as harmless.
- Hunter: The Vigil:
- It's not unheard of for Hunters, the people Heroes think they are, to form alliances of convenience between cells that dislike each other for personal or ideological reasons against the horrors in the dark - a fundamentalist Protestant from the Tribulation Militia likely doesn't have much regard for the secular, scientific compact of Null Mysteriis, for example, but at least a Godless evolutionist is somewhat better than a vampire. (Although any Hunter cell with a white nationalist or Neo-Nazi bent is not going to be able to form an alliance with the Loyalists of Thule under any circumstances, and indeed can consider themselves lucky if they survive the encounter.)
- Some Hunter cells will even ally with the less evil monsters in order to drive out something worse. However, Hunters don't generally have access to the core books from other game lines, so their ability to tell which monsters are the "good" ones isn't necessarily reliable. The Hunter term for such an arrangement is a "cancer cell".
- Mage: The Ascension has the Traditions and the Technocracy occasionally set aside their conflict long enough to take down a Nephandus or Marauder.
- Mage: The Awakening generally sees the Pentacle Orders locked in battle against the Seers of the Throne, with Banishers attacking both sides. However, when The Mad, Reaper Legacies or the Abyss-aligned Scelesti show up, all three sides will most likely declare a truce to stop them.
- Arcanacon in Australia featured a freeform called "Mars Attacks! the World of Darkness". The blurb for the game included:Will the Camarilla fight alongside the Sabbat?
Will the Garou fight alongside the Wyrm?
Will the Traditions fight alongside the Technocracy?
Will the Seelie fight alongside the Unseelie?
...and will the Malkavians fight alongside the Martians?
- Princess: The Hopeful: On the fan-made side of things, Princesses are often mentioned to dislike Beasts for their habit of hurting people as "lessons". Yet, Dark and Light reveals the two of them regularly join forces in their common hatred toward the Hunter Compacts known as the Ashwood Abbey.
- Werewolf: The Forsaken does the same thing as well, with the Forsaken and the Pure reluctantly willing to put aside differences and put down Bale Hounds or the Idigam whenever they pop up. An entire Lodge, the Lodge of the Hunt, exists to invoke this trope, bringing together werewolves who have a common Arch-Enemy.
- Magic: The Gathering has a number of scenarios:
- Almost all cards in Magic: The Gathering are divided into one of five categories, defined by certain characteristics and assigned a colour. The five colours are seen on the back of the cards in a pentangle. The characters and creatures associated with any particular colour are hated by the colours on either of the nearer points, but even they will ally to fight against a colour further away (physically and thematically) from one of them.
- This forms a significant part of the dynamic for the good guys in the Archenemy variant (since they can easily be colors that either do or would hate each other slightly less than they hate the main opponent).
- The events of the Zendikar block have the vampires, elves, humans, Kor, minotaurs, goblins, merfolk and what-have-you uniting against the Eldrazi).
- In the Scars of Mirrodin block, the Mirran forces in all five colors were forced to team up against Phyrexia... although the Black-aligned section was wiped out by the second set, and Phyrexia won in the end.
- In the Eldritch Moon set the non-mutated humans, werewolves, and vampires all team up to battle the abominations created by Emrakul, and Liliana's zombie army proves to be immune to this corruption and vital to driving them back (while none of her teammates are explicitly her enemies, few of them would team up with her unless forced to).
- In Paranoia, even if someone's ideology is directly opposed to yours (Psion vs. Anti-Mutant, Corpore Metal vs. Frankenstein Destroyers), alliances can always shift to suit the demands of the moment. You can always hose them later.
- Pathfinder: The non-canon Bad Endings of a number of adventure paths see enemies, sometimes very bitter ones, join forces to combat a new and far worse threat.
- In Rise of the Runelords, of the PCs fail to prevent Karzoug's return into the world and to sabotage the Leng Device, Karzoug's return completes a ritual that allows Mhar, the World Thunder, to be born from beneath Xin-Shalast, annihilating the city and Karzoug's forces. Although Karzoug survives by teleporting away, the narration notes that Mhar would pose such a cataclysmic threat to... everything, essentially, that the PCs might be forced to ally with Karzoug to face it down.
- In Wrath of the Righteous, if the PCs lose to the demon lord Deskari and his forces and fail to halt the next major demonic incursion from the Worldwound, then the already overwhelmed defending forces quickly collapse and the hordes of the Abyss swiftly overwhelm most of northeastern Avistan. The existential threat posed by this impending apocalypse causes a number of alliances to form as nations that have been enemies with each other for most of their existences — including the eternally-warring Nirmathas and Molthune; the crumbling empire of Taldor and its former colonies, the freedom-loving democracy of Andoran and the devil-worshipping tyranny of Cheliax; and the Ulfen warriors of the Land of the Linnorm Kings and the winter witches of Irrisen — join forces with one another to hold back the demonic tide.
- In Rocket Age when humanity started pushing its interests on Mars many warring city states put aside their differences to combat the new threat. Thus far this hasn't worked so well for them. There are also some adventures where the heroes could find themselves shoulder to shoulder with their rivals and enemies, at least for a little while.
- This comes up often between the Empire and Bretonnia, who often join forces against the Greenskins, Skaven and Chaos despite the two human nations being rivals. The Empire has also in their past wars against Chaos received some rather... unexpected help from the Vampire Counts and their undead minions, though here the dynamic is more like a rancher protecting his cattle from wolves even though he plans to slaughter them later.
- Within Bretonnia itself, the nobles are often at odds with the Herrimaults, forest-dwelling bandits who steal from the nobility to help the peasants Just Like Robin Hood. The nobles and Herrimaults, however, will still join forces or at least cease hostilities to deal with the worshippers of Chaos — the Code of the Herrimaults has a special proviso allowing them to ally with tyrants in order to oppose the Ruinous Powers.
- The End Times sees the Skaven and Chaos joining forces, the Skaven curbstomping much of the world and the forces of Order doing this on several levels — the High, Wood and Dark Elves unite after millennia of bitter rivalry and ally with the Dwarfs (who have their own deep-seated vendetta against all Elves) and the Empire, with the resulting alliance then joining up with the forces of Death (the Vampire Counts and Tomb Kings) against the combined forces of Chaos in a final battle at Middenheim to decide the fate of the Old World. Chaos wins. That didn't mean the end though.
- Warhammer 40,000 very, very occasionally has instances where the more reasonable factions will hold off on killing each other to deal with a mutual threat. For a few minutes, anyway.
- This most common variant occurs between forces of the Imperium, Eldar, and Tau against Tyranids, Necrons, or Chaos, and matching temporary alliances may occur between Chaos, Orks, and Dark Eldar, as prominently seen during Dawn of War: Winter Assault.
- The Eldar, being who they are, will often manipulate any allies they do make so that they take the brunt of the fighting (and thus casualties), in essence back-stabbing their allies during the alliance, as well as overtly so 5 minutes before its usefulness ends. Their evil cousins, the Dark Eldar, pretty much always do the same.
- It wouldn't be too much to suggest that this is the standard Ork state of being. Individual Orks are naturally hostile to everything else, even each other, but they will form into tribes to fight other tribes, and no matter how much the Ork tribes fight each other, they'll nearly always join forces to fight non-Orks.
- Dawn of War II has a new mode which exemplifies this, known as "The Last Stand", where a Space Marine Captain, an Ork Mekboy and an Eldar Farseer cooperate to Hold the Line against a swarm of enemies. The Chaos Rising expansion throws the Chaos Sorcerer and the Tyranid Hive Tyrant into the mix of heroes in the play mode, which technically cements — if it wasn't apparent with the widely opposing team we had before — that the game mode is not to be taken as canon, especially when a loyalist Marine cooperates with a Chaos Marine in any way.
- Rules for the 6th Edition allow "allies"; if the player's army allows, they can take a HQ and a Troop choice (or more if they really want to) from another army. Specifically, the categories Desperate Allies and Unholy Alliance allow players to invoke this trope if they want. The example given involved the Blood Angels fighting alongside the Necrons to stop a Tyranid invasion, without either side backstabbing the other, which led to many cries of "WAAARD!!!" among the fandom. Many of the alliance categories also seem rather unintuitive, though there's usually an underlying logic to it as of 7th Edition.
Enemy Mine / Tabletop Games