BlueHeavenHero
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You made a mistake, dear BlueHeavenHero. It's not necessary to explicitly specify passing nil as a parameter (except in rare cases, which I can explain), as any undeclared value is initially considered nil. That is, the last three (four) nil values can be omitted altogether. Furthermore, REGION_ENTER_... is a variable with a mnemonic name that stores the trigger's ID number. And this number can be passed manually, as Loli Nikita did. Of course, if he made a mistake with the number and 6 refers to the trigger that changes the quest state, then you are right.
That's the kind of assistant I am.
After one UNpleasant incident in a script, I always specify all nil values, and I practically don't use numerical values.
By the way, regarding the region and battle, this is the simplest function, in my opinion.