The throne resembles a throne made of a black steel and silver, with black silk. When sat upon you can speak a command word to awaken it. After-which the throne gains the statistics of a hydra and one's heads pop out of the back, but with a movement speed of zero. When the hydra is slain the throne cannot be awakened for 2d10 days.

Sentient 

The throne, when awakened has a mind bent on killing everything but what it is summoned to guard, and it's allies. It get's a strange satisfaction from doing it's duty.