Took me a bit to find out how to use multiple timelines in game maker. Still didn’t find anything obvious.
Create a global time line variable for the second. Before using it, make sure it is a valid timeline to use at some point.
global.timeline2 = timeline_add();
Use the with clause to utilize the secondary timeline. This will let you run a second time line at the same time.
timeline_index=[NAME OF TIMELINE];
I am using it for incoming shmup objects on paths.