Quick answer: Godot 4 AnimationTree showing the right blend in preview but not applying to the Skeleton? AnimationPlayer property must point at the correct Skeleton path - check the assigned root and bone paths.

BlendTree preview shows a walk-run blend smoothly. In game, the character T-poses.

Set AnimationPlayer path

On the AnimationTree node, Anim Player must reference the AnimationPlayer that owns the clips. Without it, the tree computes but never outputs to bones.

Check track paths

Each clip's track paths must resolve from the AnimationTree's perspective, not the editor's. Relative paths (../Skeleton3D:position) drift between scene hierarchies.

Enable the tree

$AnimationTree.active = true

The tree doesn't tick by default. Common cause of 'preview works, runtime doesn't'.

“AnimationTrees are a graph that needs an output target. The target is configured, not implied.”

Build one canonical character scene with a known-working AnimationTree config. Derive new characters from it; you'll skip 80% of these bugs.