I spawned him intentionally first try today by killing all the rats in the pit and the hall to Overlord. He showed up in the hall to the overlord. He dropped Gloomchain Boots.
Just dropped this incredibly easy mob on 1/31/08 at around 3:30am... Not that he drops anything important, but someone stated that he's "rare" so I decided to post the last time I saw him, incase someone wants that 10% haste aug like I did.
Very bottom of the pit with horde of diseased rats and few gobbys. Spawned on me, dropped regular rat loot (ears and a fur), along with Gloomleather Bracer. =p