How brief? Twelve very short seconds. Here, we have yet another video detailing the prototype version of Frost Man's stage from Mega Man 8, the elevator shaft section to be precise. Take note of the various beta sound effects (elevator, Mega's hop, Charged Shot, etc.) and of course, the unused BGM. Oh, and no Battons in sight (final build had Battons attacking you while elevator proceeded upwards)
On a related note, a few PRC readers out there are currently in the process of "hunting down" this particular prototype build. They got a few leads, but have yet to hear anything from the source of the prototype. If you happen to know of it's whereabouts, give me a holler.