This image appeared on Sculptech Studios' website on the Halo 2 page. It might be an as-yet-unseen Covenant species. It was later removed.

Luckily, Halo Planet snagged it. Sculptech lists both Microsoft Game Studios, makers of Halo, and Joyride Studios, manufacturers of Halo toys, as clients. It could be from another client... except he's holding a plasma rifle. From the head, it could be a Prophet, outside his chair, and without its robes... but it doesn't look "frail". A bunch of people at HBO contributed to finding this.