You must have code in there to make the avatar do what’s going on in the video.
As indicated in the BasePart.Velocity link I put up and by @heII_ish, if you put a Velocity in a Part it doesn’t care which way it faces because Velocity works on the X,Y,Z axes of the world, not the X,Y,Z axes of the Part.
I think you may be looking at BodyThrust:
Velocity is relative to the origin, 0,0,0. It doesn’t account for the rotation of the specific part but 0,0,0. If you want the velocity to be where the part is facing, you can simple use CFrame.LookVector and multiply it by a certain number which will act as the “speed” of the velocity.