Steps
1. Have a Pikachu with the below expression. If it does not have it, either keep making it faint (if happiness too high) or use Pikachu happiness oversight (if happiness too low) until it can have it (or manually adjust D46F to a value such as 0x4C). This also assumes that no special emotions (such as bucket Pikachu, scared Pikachu) are active.
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.
If the glitch is used immediately afterwards, it can cause the game to freeze with static playing. This occurs even after saving and resetting the game. To avoid this, Fly (or Teleport?) away before performing the glitch again.