They're playing chess, and yet at the same time they're playing a game of cat and mouse. The cyber Doctor is inside his head, seeing his memories and targeting the worst, dragging up all the old pains again.
Susan banging on the door of the Tardis, screaming for her grandfather as he left her behind, Jamie crumpling to the floor after a redcoat shot him through the leg. The sad look on Sarah Jane's face as the time lords made him leave her behind on Earth as he was made to go back to a planet that he hadn't called his home in a long while. The sad loss of Adric and his bravery, all of those K-9s he had lost over the years. The time war; Gallifrey burning, Rose, bad wolf bay, the daleks. Jack and his soldier friend Algy and misfit companion Girly. Donna with no memories, the cannibalised Tardis, the 2 times that the Master had died. Rose, trapped forever in Pete's world again, cyber men, Martha. Amy and Rory, brilliant Ponds; Brian and his loss of son and daughter in law- River Song in the library.
Everything came together in a big muddle and he screamed in pain, maybe being the cyber doctor was better, no pain to feel. But then there was Clara, the impossible girl, a whole lot of enigma in a skirt slightly too tight. The Doctor fought back against the other half and carried on playing chess.