The Corridor Creeper is a reward for completing all 8 layers of Torghast, and it allows you to mount in the Maw. Let the whining begin.
Since this doesn't seem to have been posted on MMO Champ yet, here's the Wowhead article.
https://www.wowhead.com/news=318196/...-mount?webhook
I think this is great, Torghast doesn't look bad at all so it's basically a free mount with a great perk.