If a Pokémon has zero maximum HP (but not 0/0 HP), attempting to view the party or its summary may result in a game freeze.
The game will lock up:
If the user's Pokémon:
After "Wild (POKéMON) appeared!" even if the Pokémon isn't in the first position. After "Go! (x)" if the player encountered a Trainer and the Pokémon is in the first position. After opening up the party. After switching the relevant Pokémon. (can be avoided if an above 0xFF hides the Pokémon)
If the opponent:
After "Wild (POKéMON) appeared!". After selecting a move. After closing Fight, Item or PkMn. If PkMn is closed when the lock up occurs the party's menu sprites become invisible.