How to play ROM hacks

So, congratulations! You’ve downloaded a ROM hack from the ROM Hacks Studio, Progressing ROM Hacks or Sideshow Showcase! Playing your fangame is straightforward:

1. Download the patch for the hack you’d like to play.
   These patches come in formats including .bps, .xdelta, .ups, or .ips. As a patch, it’s only one of the things you’ll need to play the game.
2. Download the ROM of the game required to patch.
   The ROM hack is the other half of what you need to play a ROM hack. For legal reasons, game ROMs (and patched versions) can’t be uploaded onto PokéCommunity, so you’ll need to search the internet for them.
3. Patch the ROM using a patching tool.
   ROM Patcher JS is recommended — it works entirely in-browser and puts the patched game straight in your downloads folder. If you receive an error, see below!
4. Open the patched ROM in the emulator of your choice.
   If you’re on a computer, mGBA is your best bet for playing nearly all Game Boy and Game Boy Advance ROMs, including fangames.

Some patches and ROMs will come compressed in ZIP/7z/etc. files, and will need to be uncompressed before you can patch them.

This guide is lovingly made with contributions from flowerchild, professor plum, bobandbill, SatoMew, SBird, Lunos, Brom, ExpoSeed, Adrevi, and the ROM hacking staff.