Shapeless lump of Stone
This is actually a Figurine of Wondrous Power: Obsidian Steed.
Only careful inspection reveals that it vaguely resembles some form of quadruped. On command, the near-formless piece of obsidian becomes a fantastic mount. Treat it as a heavy warhorse with the following additional powers usable once per round at will: overland flight, plane shift, and ethereal jaunt. The steed allows itself to be ridden, but if the rider is of good alignment, the steed is 10% likely per use to carry him to the lower planes and then return to its statuette form. The statuette can be used once per week for one continuous period of up to 24 hours. Note that when an obsidian steed becomes ethereal or plane shifts, its rider and his gear follow suit. Thus, the user can travel to other planes via this means.