The Monk's TARDIS

The Monk's TARDIS was a Mark IV TARDIS owned by the Monk.

History
Mortimus, unlike the First Doctor at this time, had a functional chameleon circuit and directional unit. After visiting several other points in Earth history, he landed in 1066 Northumbria, and having a working chameleon circuit in his TARDIS, disguised it as a stone sarcophagus in his monastery. After learning the Monk's plans to alter history, the Doctor sabotaged his TARDIS, making it the same size inside as outside. This made it impossible for the Monk to get inside it. (DW: The Time Meddler')

The Monk later fixed the dimensional controls. On a later adventure on the volcano planet Tigus, Mortimus's ship turned into a large rock. Meeting again in ancient Egypt, the First Doctor changed it into a police box so Mavic Chen and the Daleks would confuse it with the Doctor's own TARDIS. He also stole the Monk's dimensional controls so the Monk would re-materialise in a random location. The Monk ended up in an icy planet with his TARDIS disguised as a block of ice. (DW: The Daleks' Master Plan).

When the Fifth Doctor next encountered the Monk, he had voluntarily re-configured his TARDIS into a police box. The Monk had the top of his ship's roof blown off by a sonic cannon by Ice Warriors. (DWM: 4-Dimensional Vistas)

The Seventh Doctor met the Monk again in 1976 London. Mortimus, posing as a record executive, had turned his ship into a desk, complete with scraps of paper. The paper retained some of the special qualities of his TARDIS, allowing the Doctor to use paper from the desk to return to Earth after the Monk attempted to abandon him on the same icy planet he had previously been trapped in revenge for his past defeats. (NA: No Future)