The Master in the Matrix:
The Doctor's nemesis, The Master, appears before the court from the Matrix.
The truth about the Valeyard:
The Doctor denounces the Time Lords as decadent and corrupt. The Master, present at the trial via the Matrix viewer, alleges that the High Council took advantage of the Doctor's blundering into the situation on Ravolox by making an arrangement with a future version of the Doctor - the Valeyard - to falsify evidence against the Doctor in return for his remaining regenerations. The Master claims that the Valeyard is the distillation of the Doctor's darker side, from between the Doctor's twelfth and final incarnations.
The Original Matrix:
Glitz fails to save the Doctor from quicksand, only to witness the Doctor resurrect himself. But as the Doctor explains all of this a bad joke in the un-reality of the Matrix. The Valeyard appears and explains to the Doctor why he needs to destroy him.