False Appearance

If the golem is embedded in a window and motionless at the start of combat, it has advantage on its initiative roll. Moreover, if a creature hasn't observed the golem move or act, that creature must succeed on a DC 18 Intelligence (Investigation) check to discern that the golem is animate.

Immutable Form

The golem is immune to any spell or effect that would alter its form.

Regeneration

The golem regains 10 hit points at the start of its turn. If the golem takes bludgeoning or thunder damage, this trait doesn't function at the start of the golem's next turn. The golem is destroyed only if it starts its turn with 0 hit points and doesn't regenerate.

Unusual Nature

The golem doesn't require air, food, drink, or sleep.