Emulators in games
Some video games were developed with emulators built into their ROMs. Sometimes they were made to only run one game, or were capable of running other ROMs through hacking.
Nintendo 64 Games
Goldeneye 007 (ZX Spectrum Emulator)
GoldenEye 007 contains a fully-functioning ZX Spectrum 48x emulator that was discovered in 2012. The game contains 10 ROMs, all of which were made by Rare. You can read more about it here.
Pokémon Stadium GB Tower (Super Game Boy Emulator)
It's possible to play the Game Boy Pokémon games using a Transfer Pak by putting Pokémon Stadium in GB Tower mode. This software emulator can boot many other Game Boy and even GBC games in SGB mode, but there seems to be a mechanism to detect the three officially supported games, and according to this thread on the KRIKzz forum, it's possible to circumvent the checks in another ROM with a vanilla Transfer Pak and unmodified North American copy of Pokémon Stadium. Not many useful tools are available, but in theory a romhack of Stadium could disable these checks (considering they're documented) and could even be placed in Stadium's ROM instead.
One notable thing about this emulator is that it contains an alternate revision of the CGB bootstrap that hasn't been used anywhere else.
Sega Smash Pack Volume 1 (Megadrive Emulator)
This compilation of Genesis games for the Dreamcast contained a Genesis emulator and a plain-text document on how to use it. You can read the full story about it here.
Download: Sega Smash Pack - Echelon
The Legend of Zelda Collector's Edition (NES / Nintendo 64 Emulator)
Nintendo released a promotional disc with some GameCubes that contained some of the mainline entries in The Legend of Zelda series and a demo of Wind Waker. To get the NES and N64 games running, Nintendo used in-house emulators to recreate the original experience, albeit with occasional crashes and analog sensitivity being a tad excessive for what the original console really offered.
NES emulation was already done for the GameCube remake of Animal Crossing, where they modified some FDS BIOS images, didn't support iNES headers and only a limited amount of mappers. The N64 emulator is more interesting; it was later extracted in a standalone format and a custom ROM injector was implemented.
Compatibility is very low, with only these games confirmed working: Super Mario 64, Mario Kart 64, Star Fox 64, Kirby 64 (partially working), Zelda: Majora's Mask, Zelda: Ocarina of Time, Zelda: OoT Master Quest, Duke Nukem 64, Mace: The Dark Ages, Wave Race, Star Soldier, Pilot Wings. Possibly other games too.
Download: Nintendo 64 Emu
Pokemon Channel (Pokemon Mini Emulator)
Like Stadium, Channel contained an emulator for playing Pokemon Mini games on the GameCube. It was later stripped out of the game as a stand-alone Pokemon Mini emulator for the GameCube. Later Pokemon Mini emulators have based some of their work on this feature.
Download: SHizZLE's Pokemon Mini Emulator
Pokemon Box: Ruby and Sapphire / Naruto Collection (GBA Emulator)
For some reason, these compilations tried to claim they worked by streaming the original cartridge data through a Link Cable in order to play them on a bigger screen. And while it is true that they require the GBA cartridges, the actual data the game needs is already on the disc itself, as the game uses a GBA emulator Nintendo developed in-house to run the games.
Compatibility is poor though - the emulator heavily modifies the game's code. When the extracted ROMs are played on regular GBA emulators, or regular non-32 MB GBA ROMs are injected in the compilation, the games do play but suffer a variety of glitches mostly involving sound.
Fight Night Round 2 (SNES Emulator)
Super Punch-Out!! is a bonus game included in Fight Night Round 2.
Twinbee Collection (SNES Emulator)
Pop'n Twinbee, originally a Super Nintendo title, was given an emulator for this compilation. However, the emulator they used is hacky. While the game ROM is unaltered, it was split across four individual pieces, making injections tedious but not impossible. This is similar to the approach used in the "I Love Mickey Mouse" re-releases of Mickey/Donald Mega Drive games for the Saturn.
Swapping the data with another ROM of the exact same size (like Tiny Toons Adventures) reveals occasional graphical glitches, and controller problems.
PC Engine Collections (PC Engine / PC Engine CD Emulators)
Hudson Soft re-released many of their PC Engine/TurboGrafx-16 exclusives through compilations on the PSP through emulation, and for PS3 as well on both the Japanese and North American PlayStation Stores. These compilations use top-notch emulators with many scaling options, and the process of injecting other games is easy.
For standard PC Engine cartridge releases (HuCard), the following compilations can be used as surrogates:
- Soldier Collection PC Engine Best Collection
For PC Engine CD games, the above compilations can be used in addition to:
- Far East of Eden Collection
- Ginga Oujou Sama Densetsu Collection
Dump the UMD to ISO format with the method of your choosing (like CFW), and open the ISO's contents with UMDGen.
The game images are usually under the directory
- PCE HuCard Cartridge games: PCE files. Exact same as No-Intro dumps.
- PCE CD-ROM² games: folders named something like
HCDxxxx(usually the release identifier). HCD/AT3/BIN files are inside, which are in fact a regular PCE-CD ISO in CUE/WAV/BIN format (TOC files are also used) with the WAV sound files converted to the native PSP audio format (AT3). Instructions about how to convert them can be found here in Japanese, and here's a mirror to the pceconv tool used.
- BIOS file: SYSCARD3P.PCE, needed for CD emulation. Should not be replaced.
Rename your ROMs (HuCard games) or ISOs (CD games) to match the internal filenames, and drag and drop those in UMDGen to replace the existing files (confirm overwriting existing files). You can delete the PMF videos used by the collection's gallery mode to make the ISO smaller. When you're done, go to File and Save as ISO (CSO is smaller but doesn't play well on real hardware).
You can do the same with standalone PSN releases of TG-16 games which were made available as well on the PSP/PS3/Vita PSN. You just have to sniff the PKG, extract it, decrypt it and replace the PCE files or ISO dumps just like with the other collections. After that, you just have to re-encrypt them and put the files on your console to play those. More detailed instructions exist on Wololo.net.
NES Remix Series
NES Remix, NES Remix 2, NES Remix Pack, and Ultimate NES Remix used an emulator called Heritage. NES Remix uses Heri1. NES Remix 2 uses an updated version called Heri2. Ultimate NES Remix, the last of the NES Remix series, uses HeriC. The NES Remix Pack has both Heritage 1 and Heritage 2 and switches between them depending on the selected game. This is the first official emulator to have wacky effects. No ROMs were tested.