Basically it's a device that fuses multiple objects together, kind of like Fusion Dance. Works by either shooting a beam or placing the objects into a machine. May also work in reverse. Sometimes, the effect is unintentional and probably not the main purpose of the device; Teleporters and Transporters are particularly prone to becoming Merging Machines when something goes wrong, especially in cases such as Tele-Frag.
Not to be confused with Combining Mecha.
- In JoJo's Bizarre Adventure Part 8 (JoJolion), the Wall Eyes are a geological phenomenon that have this effect on objects buried in the ground near them. One character demonstrates this by burying a lemon and an orange, then digging them up and cutting them to reveal that they've swapped segments. Later it's revealed that this has nothing to do with the Wall Eyes, and the ground has had this property for generations. It's also responsible for the creation of protagonist Josuke Higashikata, who's the merger of two men, Yoshikage Kira and Josefumi Kujo.
- Wapol of One Piece had this as one of his sub-powers. While the Munch-Munch Devil Fruit gave him the power to fuse himself with anything he ate, he could also fuse eaten objects with each other, creating an entirely new object. This trope is then exploited as he ends up profitting by promoting the fused objects as toys and selling them.
- There was a strip in the 1970s British Comic Whizzer and Chips called "Minnie's Mixer", which played this for laughs. The eponymous device looked like an electric food mixer, but when pointed at two objects in close proximity could fuse them together. Most often used to mix people or pets with objects. Fortunately the process was reversible.
- A case where the "merging machine" is a person: In the thirteenth issue of Grant Morrison's Animal Man series, the B'wana Beast was infected with Anthrax and it drove him a bit crazy, to the point he was using his powers to merge random animals and turning the resulting chimera into killing machines.
- The Fly is arguably based around an accidental version, merging a man with a fly (and later the man-fly with the teleporter itself). Many parodies and homages tend to fall into this trope by having multiple "mixings" take place.
- One of the Choose Your Own Adventure books based off of Super Mario Bros. called "Monster Mix-Up" used this as its primary gimmick. Bowser has a device called the Monster Mixer, which looks like a giant flying egg-beater◊, that he uses to fuse his minions together into more dangerous troops. The ending has Princess Peach consider unfusing them with a device based upon a soup strainer.
- Star Trek: Voyager episode "Tuvix". A transporter accident fuses Tuvok and Neelix together, forming the title character. They eventually work out how to reverse the process, leading to an existential plea from him equating it to murder.
- Mystery Science Theater 3000: In the "Manos" The Hands of Fate episode, Joel's invention exchange is the Cartuner, a device that takes two newspaper comic strips and combines them into something funnier than the source material. "Ziggy had Garfield neutered?!"
- Inverted and then played straight in one episode of Star Trek: The Original Series, where a transporter malfunction splits Captain Kirk into two people, one with all his more aggressive traits and the other with his more passive traits. Eventually the crew figures out what caused the malfunction and successfully uses the transporter to reunify him.
- In a failed CBS pilot a scientist developing a teleporter decides to use it to surprise his girlfriend in another lab by teleporting in with a rose and invite her out for a date, but being unfamiliar with the lab he teleports into the same location of an advanced space probe complete with AI and survival instincts she's developing causing them to merge. As a result when he's threatened the probe that's otherwise invisibly merged with him emerges in increasing degrees until when at risk of death it completely takes over looking like a vaguely humanoid killing machine.
- BIONICLE: the Spear of Fusion, which can also be used in reverse.
- Jakyou Manors/The Velvet Room/Demon Fusion Program-enhanced tech in most of the Shin Megami Tensei games, including the Persona series, function this way for combining demons, personae, swords, spell/tarot cards, and any number of other compatible things.
- There have been cases in which accepted parts for fusions have included humans (twice) and a dog. Most of the time, they remember their pasts. On the other hand, aggression level is raised and there is the question of getting a severe case of violent madness and eventual breakdown; so far, there has not been a single recorded case of a successful demon/human fusion in which the results did not present a form of sanity degeneration, either through obsessive devotion to all laws or complete and utter contempt for all of them, both reaching sociopathic degrees later on. Evil Is Not a Toy, kiddies!
- In Tymora's Luck tinker gnomes and two gods made a "fusion chamber".
- Played with in Day of the Tentacle, where, at the end, the three Player Characters have to use a single Chron-O-John to travel through time, chasing the Purple Tentacle. They come out apparently fused into a single monstrosity with three heads. Later, Dr. Fred uses an X-ray machine to scan them, revealing that they're all separate people stuck in a single shirt. Embarrassed, they separate.
- Mocked in No Time to Explain for the final level. One of the Yous suggests wielding both the beam cannon and the shotgun at the same time to enable a Double Jump, and this is somehow taken by one of the other Yous to fuse that You and Stunt Man You into one being who wields both. The fused character's profile page is even him screaming in agony.
- In Psychonauts in the Rhombus of Ruin, Raz encounters a device in a crashed alien spaceship that can split and merge objects.
- Homestuck's punch-card alchemy process lets you convert objects into punch-card codes and back, and by merging the codes, you can create merged objects.
- Kid Radd has the Chimera program, which, among other things, can merge individual sprites together. You have to be extremely careful when you set the parameters, however, or things will get ugly.
- The SCP Foundation has SCP-914, "The Clockworks". Putting two items in the input booth and running the machine on "fine" (the setting for turning things Up to Eleven) or "very fine" (typically produces something that goes even higher to the input) tends to yield outputs that combine aspects from both inputs; in one of the side-stories, 914 was fed a D-class and a 64-core supercomputer multiple times, with outputs including sixty-four small robot spiders with human faces and a human with a supercomputing brain (which was the desired output). In addition, one of its other settings, "coarse," often functions as an Inversion, separating objects into their component parts.
- The Ace Ventura animated series had an episode based around a scientist whose teleporter combined him with a fly. Later in the episode Ace is combined with Spike.
- ReBoot had an episode where a corrupted game fused Megabyte with a containment unit filled with liquid energy. It turned him into a Megatruck, and the game just happened to be a pastiche of Mad Max 2: The Road Warrior.
- One Treehouse of Horror episode from The Simpsons, where after Homer buys a matter transporter from Professor Frink (and uses it around the house to save him walking from one room to another... though it takes more effort to move the transporter booths), Bart uses it to fuse with a fly, hoping it will give him superpowers. But instead of Brundlefly, he gets the 1958 Fly (Bart with a fly head, the fly with Bart's).
- Alpha from the Men in Black series used an alien device called the Cosmic Integrator to grant him the power to fuse alien body parts to himself.