It's Princess Bubblegum's Rainicorn! In scarf form, which my sister says makes it look like a dead Rainicorn pelt.
It's about 64 inches long.
Did you know Cartoon Network is making a full-blown Adventure Time ([link]
) cartoon? I'm super excited!!
...I would very much love to give this scarf to the show's creator, Pendleton Ward, but I don't know how I'd go about doing that.
EDIT: Yaaay, I gave it to him! [link]
Thanks Mr. Muto!