From Divinity Engine Wiki
|In general, you cannot use Osiris scripting in Game Master mode. The reason is that when a Game Master mode savegame is loaded, all database facts from the savegame are deleted and the story is reinitialised from scratch. This was a conscious design decision of Game master Mode, because everything should be under direct control of the game master. You can use behaviour scripts, though.
- Osiris tutorial videos from DOS1 (the language has changed a little, but the base concepts are still the same and these videos are still 99% relevant; you can ignore the last one about dialogs, as the dialog system has changed completely)