Hello! I have some issues with animations.

Add two parameters to the Animation blend tree. float speed and bool isRunning. If the former is below 0, transition to the moving backwards animation. If shift is pressed, set isRunning to true and transition to the runnign animation instead of walking. Both speed and isRunning would be set in your script via Animator.SetFloat/SetBool when appropriate.

in the Animator controller when you are changing between trees, select the arrow between the trees and set the animation as really want (how it will change from one animation to other, how'd it take and the behavior while it's changing)