Shummrath

Shummrath was an unusual pit fiend in Avernus, first layer of the Nine Hells, in the late 15 century DR.

History
Once Shummrath was a powerful pit fiend until he failed to show deference to Bel and the archdevil punished him by imprisoning the pit fiend inside a canyon of the layer. In time, only the mind of Shummrath remained inside a lake of slime but some water from the River Styx spilled inside, weakening Shummrath's mental integrity.

By the, Shummrath had only a memory span of thirty seconds and repeating just a single thought constantly. However, if freed from the Styx, Shummrath reformed as a pit fiend in 48 hours and tried to have his vengeance against Bel.