Quick answer: Construct 3 physics objects pinned together jittering? Two physics bodies + a Pin behavior fight each other — turn one body into a sensor or use a physics Joint instead of Pin.
A sword pinned to a hand jitters violently when the hand moves. Both are physics-enabled and Pin tries to lock them while physics tries to separate them.
Pin vs Physics
The Pin behavior is a kinematic snap each tick. Physics resolves collisions and forces between bodies. Two physics objects pinned together = fight per frame = jitter.
Use a Physics Joint
The Physics behavior’s Create Revolute Joint / Create Distance Joint actions bind two bodies with proper physics constraints — smooth, no jitter.
Make One Non-Physics
Alternative: disable the sword’s Physics behavior, keep only Pin. Sword follows hand kinematically — cheap and stable, but the sword can’t generate physics forces on collisions.
Verifying
Pin and physics work together without jitter. Swinging the sword swings the pinned object smoothly.
“Pin + Physics fights. Use a joint, or disable physics on the pinned object.”
Reserve Physics for things that need physical interactions — HUD elements, sticky attachments, decorations don’t. Smaller physics scope = faster sim.