The Valeyard's TARDIS was a twisted future version of the Doctor's own ship, (PROSE: Matrix) although another account indicated it might have been another TARDIS entirely. (AUDIO: Every Dark Thought)
It appeared as a stone sarcophagus with the Doctor's thirteen faces engraved in it. (PROSE: Matrix)
When the Valeyard visited Victorian London, it took the form of a costumers, where he created duplicates of various pieces of clothing worn by the Doctor and his companions. (AUDIO: Stage Fright)
By the time he met Bernice Summerfield, the Valeyard had taken apart the whole console to find a fault preventing the TARDIS from travelling correctly, either in the lateral stabilisers, the helmic regulator, or both, and he could not locate the Cloister Bell to disable it. Its translation circuit was less reliable with written languages. Some of the items it contained included tea, fruitcake from Christmas, 1888, and a knife used by an 18th century Chinese assassin. Benny guessed that the TARDIS controls wouldn't respond to the Valeyard because he wasn't a "proper Time Lord." (AUDIO: Every Dark Thought)