No problem; the game’s quite fun so it was a pleasure to play test.
I was originally going to suggest some quick code to allow some easing in and out of the velocity while running, but it’s actually better if you’re willing to research damping because it does really help simulate friction, so you’d be able to set a number for air friction, water friction and different numbers for specific blocks the player collides with, like ice or grass.
I haven’t touched Game Maker in years, so I don’t know if there is just an internal function for handling this, or if you have to code it yourself, but even if you have to code it yourself; it will probably come down to a “lerp” function (Linear interpolation) and looking up something like “frame rate independent damping”. It’s not as complicated as it sounds and it’s super useful because you’ll probably use it in a ton of future projects.