I think that during the climax, manifestations of all the Doctor's main incarnations make cameos as Guardians of the Edge, alongside Jo Martin's Fugitive and John Hurt's War Doctors, solving the mystery of why David Tennant's 14th Doctor has returned to an old face, because NPH's Toymaker is the culprit! They find Ncuti Gatwa's 15th Doctor's soul trapped inside their conciousness unable to break through as a result while 14 is fighting the Toymaker in the real world, "Will someone tell me what the hell is going on here?!", to which the other Doctors explain the dire situation to him. 14 communicates with his other selves via telepathic contact, and they initiate a risky, dangerous plan to defeat the Toymaker for good, but it just might work, using regeneration energy as a weapon against him, because being the Timeless Child their endless supply will be too much for him to handle. Seeing as how regeneration energy has the power to make you older or younger, they also plan on taking advantage of this specific ability against the Toymaker, before the Guardians of the Edge manage to physically manifest in the real world temporarily. Including 14 as well as 15, all the Doctors use their combined regenerative cycle together to age the Toymaker to death until nothing is left of him but skin and bone, diminishing his cosmic powers while banishing the Toymaker into the Void forever! 14 wakes up sometime later all alone, before looking at his hand which glows with energy, revealing that the plan worked and the regeneration has been triggered automatically as a result of being corrected now there is no Toymaker to manipulate it. He returns the TARDIS to Earth, having dinner with the Noble family (Catherine Tate's Donna gets to keep her restored memories by the way!), before saying a fond goodbye for good, and finally regenerates into 15 after his last words "I am ready to go", which leads into series fourteen...
And if you are wondering how I think all the former Doctors could return as Guardians of the Edge manifestations, well first of all Jodie Whittaker would have been heavily pregnant during the 60th's filming, but only needs to show her face anyway if you really think about it. Peter Capaldi, Christopher Eccleston and Hurt's faces would be edited on via CGI as unfortunately Hurt is no longer with us while Capaldi does not want to make a return as well as Eccleston, so voice impressionists can also be used for their Doctors if that makes sense. Tennant would be playing double duty as 10, while Matt Smith, Paul McGann, Sylvester McCoy, Colin Baker, Peter Davison, Tom Baker and Jo Martin can all return themselves just like some of them already did during The Power of the Doctor as Guardian manifestations. David Bradley would portray William Hartnell's 1st Doctor as he is obviously the best person to do that, while Patrick Troughton's son David and Jon Pertwee's son Sean can stand in for their late fathers because they both look just like them! What do you think about my insane theories, I know how truly crazy it all sounds but if there is any way of every former Doctor making a cameo together during the 60th anniversary specials this is it! Yes RTD would not have known about the Guardians of the Edge while writing the 60th, but he did actuay watch TPOTD in full during filming, so who's to say he didn't rewrite a portion of the episodes to include the Guardian manifestations afterwards which resulted in all those reshoots? So yeah, what do you think, ADmiralPRESENTS??
