So, I was making some paths for my enemies to follow, specifically, a path that sort of looks like a bouncing ball. I said soft of. It's Graph Paper Shooter, not a ball bouncing simulation.
Since it was so simple, I just started drawing on the path editor.
I was not careful to make sure my first point was zero. That led to some unexpected behavior.
The idea was that these particular enemies would leave the spawner and orient their path such that it pointed in the general direction of the player. For this to work, I needed to set the variable "path_orientation" after I told the object to start following the path.
Here's the thing: when setting path_orientation in GMS2, the path will rotate around the 0,0 point (x=0, y=0) as defined when the path is created in the editor. It does not rotate or orient around the first point of the path, as you might expect. The documentation for path_orientation does not mention this. The docs for path_rotate (an actual function) mention this, but path_rotate rotates the original path object, not the path you're using.
So, just a heads up. When you use path_orientation and your paths are going completely the wrong direction, check that your path starts at the origin.