– Google is your friend, but know the legal risks.
SM64 Co-op DX is you load into an emulator. It’s a standalone PC game built from decompiled SM64 source code. You don’t need an emulator, and you don’t “patch” a ROM. sm64 coop dx rom
Here’s a full post explaining and the ROM situation clearly and accurately. Title: SM64 Co-op DX: Do You Need a ROM? How to Set It Up Correctly – Google is your friend, but know the legal risks