Quick answer: Godot 4 RigidBody mass effectively doubled after a runtime shape change? Mass property's multiplier reapplied on shape recompute - explicit set after change.
Object's collision shape switched; mass should stay 100; effective mass becomes 200.
Reset mass post-change
body.change_shape(new_shape)
body.mass = 100Force mass back; multiplier reset.
Or use linear_mass directly
Bypasses the multiplier. Direct kg value.
Audit shape changes
Each runtime shape mutation: mass behavior documented.
“Mass and shape interact. Changing one resets calculations for the other.”
If your physics has variable shapes, the mass reset after shape change is the discipline.