CC5C Rival's is a Pokémon Yellow exclusive glitch similar to Rival's effect. However, the glitch requires a way of locking address CC5C (wPikaPicUsedGFX) to 0x0A; hence like glitches such as Pikachu glitch emote arbitrary code execution, it currently requires arbitrary code execution to begin with.
1. Have a Pikachu with the below expression. If it does not have it, keep making it faint to lower its happiness until it can have it.
2. Use arbitrary code execution to lock CC5C to 0x0A. OAM DMA hijacking will loop arbitrary code automatically.
3. Talk to Pikachu. A blank text box should appear.
4. Open the start menu and close it. A corrupted region should appear where the text box was, and it is now possible to walk through a limited number of walls like Rival's effect.
- Torchickens (documentation)