: Join up to 16 players in a single game session.

The ROM is a modified version of the game's code, which allows players to experience the game in a new way. The Coop DX ROM is designed to be played on a PC or other device using an emulator, which mimics the original Nintendo 64 hardware.

However, the "story" of Co-op DX is defined by how it expands this premise for multiple players:

Old multiplayer hacks used to crash when the "Big Boo's Haunt" door appeared. The top Coop DX build has fully synced boss fights and cutscenes.