Auxiliary Class/Pet Hotkey Slot

[Brandubh]

I vaguely remember seeing a second hotkey box adjoined to my Stealth box several months ago. I disabled it, and now have no idea how to re-enable it, what addon it was or even if it exists still. Now, having changed to Assassin spec, would love that extra little window for Cold Blood. Does anyone know or remember anything about this hotkey? If so, please let me know!