If you're using the character motor, use the one in this post. It has the important settings, such as speed etc exposed so you can change them at runtime. I didn't study the game you showed but apparently he's running a bit slower before jumping , as if he redirects his momentum upwards, which is a nice detail. To do that, create a state which uses set property each frame on the max forward speed. then use an ease float action to first smoothly lower the max forward speed, and then in a new state smootly raise it back to its' default value.