@silverdot, your collision mask is convex (it has an internal angle at a point that’s greater than 180 degrees), and will be ignored by GDevelop. Instead the default of a collision mask covering the entire sprite will be used. That yellow triangle in the top right is there for that reason.
Instead, you can make multiple polygon collision masks in one sprite though. In the image below, there’s an “Add collision mask” button, and multiple collision masks. I’m not sure if there’s a limit though.
