From what I've seen, it crashes on the Gary battle for a lot of people (and also in my own tests). Does the Gary fight work for you?
Viewing post in (NOT) Pokemon: Misty Orange DEMO comments
Geez, that's literally the basic give item script. This is good information to have. Joiplay right now is just so finnicky with this demo (and, I'm also introducing some more complicated code for the final) that I'm going to plan to see how they update it in the next few years because if work on it now I just won't have the energy to finish the game. Hopefully, some of these errors will just been non-issues as their emulator gets better but I'm definitely going to try ironing out the wrinkles for the final release if they're not. Thanks for the report though and I'm sorry I couldn't be of more service!