How do I run a built-in function in multiple events?

You can't add two functions with the same name. But you can call a function from any event sheet in the project.

Why would you want to do that? I can call my functions from other event sheets. In fact I have a whole event sheet just for functions and call them from my main event sheet.

Example: i have a fuction making the player jumping. In another event group concerning screen effects, the same function enabled an effect. I know i could simply unifty both actions when the function is called, but for organization sake i prefer doing that (and it was possible with the function system in C2).

You should have one function doing what you want and use function parameters if you want alternations of that function.

Imagine you have 3 different versions of the same function on 3 event sheets and then you need to change huge portions of that function. Than you have to do every change 3 times instead of just one time. Also it can get messy if you forget to update some of these functions to the newest changes.

I would probably use a Boolean function parameter so that you can easily enable or disable additional function behavior.