Place this clip at the start of a reveal sequence, then follow it with a bass drop sound effect as the completed form takes its first step, and add a reload gun cue only if weapons appear in the next shot.
Über diesen Sound
This clip is Blackout's full transformation sequence, about twelve seconds of layered gears, hydraulics and folding metal as the helicopter reshapes into a robot. It feels massive, tense and intimidating, building mechanical power rather than a quick jump scare. It comes from the 2007 Transformers film.