Whether it’s an Easter egg, a joke character, or just a little nudge at a competitor, developers love slipping the odd reference to other games into their own. Sometimes though, they go beyond just slapping a Dopefish on a wall or quipping about a ‘doomed space marine’, and we get to see our heroes stride into entirely new, often completely inappropriate new worlds.

Here are a few of our favourites, along the ones that caused the most ‘wait, what?’ blinking on discovery. 

Guybrush Threepwood, Mighty Jedi

Yes, he can hold his breath underwater for ten minutes and quip his way through any sword-fight… but only The Force Unleashed II let him try his luck with a lightsaber. Turns out that you don’t need a sharp wit if you’re waving around two of the universe’s deadliest glowsticks and aren’t afraid to use them. Guybrush Threepkiller is so famous in-universe, he even has his own statues. We’re almost positive that’ll be brought up at some point in the next movie. After all, Rey does need a new teacher. Just as long as Elaine never finds out about it. 

Final Fantasy makes history in Assasin's Creed

Obviously, everything in the Assassin’s Creed series is meticulously researched and true to life, especially the alien gods and the time Ezio punched the Pope. Write it all down in your history homework! Which means that, while aliens might not have built the pyramids, they definitely got up to a bit of chocobo racing on the side. That’s according to this crossover, where Assassins ended up in Final Fantasy XV, while its villain ended up pounding sand for a bit before being dragged back to his own game by a hastily summoned Bahamut. There’s even a stuffed Moogle lying around in case you feel lonely after they’ve gone, and some fancy weapons to keep and confuse archaeologists for a few thousand years. Along with that Stargate, obviously. 

Commander Keen hangs about in Doom II

There’s a few odd appearances in Doom 2, including the severed head of John Romero as the end-boss, and a trip back to Wolfenstein 3D in the secret levels. By far the strangest thing though is what lies behind those: former id star Commander Keen… murdered and hanging from meathooks. The story goes that Adrian Carmack was the childkiller in question, having chafed at making cutesy games instead of enjoying himself with blood and guts. However, that was not enough to get rid of the boy-genius forever, for both John Romero and Tom Hall have confirmed that Commander Keen, real name Billy Blaze, is in fact Wolfenstein hero BJ Blazkowicz’s grandson… and father to the Doomguy. What a strange family tree. 

Earthworm Jim digs into Battle Arena Toshinden

He’s the world’s mightiest worm! He fights aliens! He travels galaxies! He gets flattened by a lot of cows! And he’s one of the few 90s mascots to actually be awesome, starring in two excellent platformers, one surprisingly good cartoon series, and… well, let’s not mention the sequels. Like Bubsy, 3D was not kind to Earthworm Jim, though unlike Bubsy, people actually cared. His most successful jump into the third dimension turned out to be this Easter Egg in the PC version of Toshinden, where with the help of his super-suit and a really big club, he was finally able to make the future of gaming eat dirt. Pound them into the ground. Bury himself in glory. Be cut in half and yet… no, wait. Not that one. But it was still as good as fans were going to get.

Everyone plays Poker Night at the Inventory 

Easily the most ambitious gaming crossover in recent memory… and it’s all about hanging out between games. Telltale’s Poker Night series combined, amongst a few others (deep breath) The Heavy from Team Fortress 2, Max from Sam and Max, Strong Bad from Homestar Runner, Tycho Brahe of Penny Arcade Adventures and also some webcomic whose name we forget off-hand, GLaDOS from Portal, Brock Samson from the Venture Bros (not a game, but never mind), Claptrap from Borderlands, Sam from Sam and Max replacing Max from Sam and Max, and Ash from The Evil Dead. Phew.

They weren’t great poker games, but that wasn’t really the point. It was about the banter between the different competitors as they sat back and shot the shit without the customary heavy artillery. We could also have had members of the cast from The Walking Dead and Back to the Future, but they were deemed unsuitable for the atmosphere. They didn’t want anyone crying, or any kids seeing Doc and Marty in a sweary environment. A pity. When the game revved up, they could have seen some serious shit.

Portal 2’s Space Core invades Skyrim 

When Bethesda showed off DLC for Oblivion, it was horse armour. And everybody laughed. Come Skyrim, the laugh was far more positive. One of the earliest additions saw the exiled Space Core (spoilers for a decade old game there) crash-land in Tamriel, still just as eager to explore SPAAAAAAAACE. Going bizarrely unnoticed by the locals, all probably fretting about that whole dragon invasion thing, it came crashing down in a plume of smoke. Pick it up and it still kept blinking and talking in your inventory, delivering… well, not very varied dialogue. In summary:  “Space. Space. Space!” And yet, still it was less annoying than all those guards and their epic tales of glory curtailed by the sudden impact of a ballistic stick to the lower-leg.

XCOM defends Civ V: Brave New World

What does XCOM do when there are no aliens to fight? Apparently, they learn to ****ing shoot straight. The XCOM Squad in Civ V is an elite tactical unit that gets the job done, air-dropping into friendly territory and laying down the law. Specifically, Thou Shalt Not Screw With XCOM. In the absence of aliens, they have their eyes set on "Giant Death Robots," and are happy to act as shock troopers or defensive units while they watch the skies and await their destiny. But since there are apparently no aliens interested in Earth during the Civ games, they’re probably going to be waiting a while. Should have taken the flight to Alpha Centauri.

Princess Rosella favours Leisure Suit Larry 3

Sierra On-Line loved its in-jokes. Not one but two sequels (this one and Space Quest III) ended with the characters somehow finding their way to the developers’ own offices for a chat with studio leads Ken and Roberta Williams, with Larry also taking trips to a Westworld style factory where adventure heroes are rebuilt after every stupid death, complete with King’s Quest’s King Graham being readied for duty, and finally showing up in the Old West for a cameo in Freddy Pharkas Frontier Pharmacist. By far the strangest cameos came at the end of Leisure Suit Larry 3, where the trip to Sierraland involved trekking through scenes from games like Police Quest and Space Quest 2, before meeting Roberta Williams directing a particularly annoying scene from King’s Quest IV, in which Princess Rosella is trapped in the slobbery mouth of a giant whale. Strange.

Frank West covers Lost Planet: Extreme Condition

He’s covered wars, you know. But oddly, Dead Rising’s original and best hero doesn’t seem to know how to cover himself in this odd outing. Despite Lost Planet being set on a frozen world, everyone’s favourite photographer show up not only without his camera, but also without his trousers. Somehow avoiding hypothermia, he runs around in nothing but underpants, while still managing to rain destruction on the armies of insects happy to not have to peel their food for once. What a trooper. 

Scorpion goes mental in Psi-Ops

Fighting game characters are probably the most cameo-friendly of all, whether it’s a full game like Mortal Kombat vs DC Universe, or bonus combatants-without-a-k-because-that’s-how-it’s-spelled in the likes of Injustice. But they show up in other games with curious regularity too. Lightning god Raiden for instance showed up in Unreal Championship, while invisible fighter Reptile could have popped into basically any game. Ever seen a flicker on your screen playing, say, Fortnite? As far as you know, it might be him.

But still, this was an odd one. Even though Midway was the publisher of both MK and Psi-Ops, it’s a bit of a leap from fighting game to third-person action game. Sadly, just wearing his palette-swapped ninja outfit didn’t actually make you the world’s clingiest fighter. He still had to swap out his “get over here!” attack for regular guns. On the plus side, having to beat every character in the game two out of three times would have gotten pretty darn tiring.