The TARDIS is a time machine piloted by Dr. Whooves, that functions as both residence and vehicle, and is shaped like an Equestrian Police Public Stall Barn. It's larger on the inside than on the outside, and possesses a vast, complex interior, despite being about the size of a phone booth on the outside. In addition to The Doctor, it also serves as a residence for Dr. Whooves' adopted son, Tornado Bolt. The TARDIS normally resides behind the Treebrary, a short ways off from Spike's garden, parked directly under a banana tree.
Though not immediately apparent, the TARDIS is both alive and sentient, just unable to properly communicate in a way that can be comprehended by most life forms other than another TARDIS. The Doctor is constantly working to repair, rebuild, or improve the TARDIS systems when not off on an adventure, or helping out around Ponyville.
The following section will focus on the TARDIS' history in the events of the RP. For more detailed information on the TARDIS, visit the page over at Tardis Wiki , and just put a pony spin on it
References to the TARDIS can be dated back to the most early recordings of history, even back to the paintings of cave ponies. Its unique shaped has caught the eye of many historians and conspiracy enthusiasts over the years. According to Marigold, after performing a lick taste test, the TARDIS tastes of a combination of plant, animal, and mineral, all at the same time.
Before taking the throne, Princess Celestia and Luna both travelled in the TARDIS, calling it their home during their travels with the 8th incarnation of the Doctor. Due to their time together, and the nature of the royals, the TARDIS will often allow them access to its interior without the use of a key as a sign of trust. Celestia herself seems to share a link with the conciousness of the TARDIS that even the Doctor is unable to achieve.
However, even with this friendship, and after being pranked by both individuals, the TARDIS itself entered the New Prank War siding with the Doctor against Celestia, and Rainbow Dash, and proved to be a formidable prankster when pushed. Some of her tricks included flipping the spacial dimensions of Rainbow's home interior, and reverting Celestia's bedroom chambers to their "80s look." Both pranks reverted to normal after 24 hours. (as per the rules of the Prank War) With the prank war now resolved, the TARDIS has shown to have gained a respect for Rainbow Dash.