WMG / Doctor Who 60th AS "The Giggle"

The Bi-Generation occurred because the Fourteenth Doctor was still "young"

• A possible explanation for the bi-generation could be that the Fourteenth Doctor was still in the first fifteen hours of his new incarnation, assuming an hour or so for "Liberation of the Daleks", a relatively late-night arrival on Earth to deal with the Meep, and he and Donna spending an hour or so on the ship before returning to Earth to face the Toymaker (a couple of days elapsed for the rest of the world, but there's nothing to indicate that an equivalent amount of time passed for the Doctor and Donna). Essentially, Fourteen's body still had residual regeneration energy much like when his tenth self re-grew his hand, so when the process was triggered again he was able to channel that energy to grow a new version of himself.
  • Debunked via the Children in Need special. He says he used to be "this amazing woman twenty-four hours ago". He's solidified.
    • No, he says "60 minutes ago, I was this really brilliant woman". 60 minutes.

The Bi-Generation occurred because the Fourteenth Doctor under the playful effects of the Toymaker.

So it's unlikely to come up again because it was under those odd circumstances.

• Nope. The Toymaker was just as surprised as everyone else when the Doctor split in two. He even thought it was cheating to have the two Doctors team up against him. So it's not likely for it to be the Toymaker's powers to cause the Bi-Generation.

The Toymaker's other encounters with the Doctor are still valid

The Toymaker and the Doctor each agree that this encounter is essentially their second game, with the first and only previous game occurring in the Doctor's first incarnation. However, this may be explained as the Doctor's other games with the Toymaker were all basically "invalid" for various reasons;

• In "Divided Loyalties" the Fifth Doctor's game with the Toymaker is ended by outside factors, with the Doctor himself basically declaring it a tie and musing that was the best he could hope for.
• In "The Nightmare Fair" the Sixth Doctor was saved from finishing the Toymaker's new video game when his allies were able to help him trap the Toymaker.
• In "The Magic Mousetrap" the Seventh Doctor helped others trap the Toymaker by playing him in multiple games at once, so the Doctor wasn't playing the Toymaker one-on-one.
• In "Endgame" the Eighth Doctor is able to trap the Toymaker in a scenario where he's constantly playing against a duplicate of himself rather than him facing the Doctor.
• In "Solitaire" the Toymaker was already engaged in another game when he summoned the Eighth Doctor's TARDIS, so he essentially never played the Doctor on that occasion.

Alternatively, the Toymaker unwrote previous encounters when he "turned [the Doctor's] personal history into a jigsaw", the exact petty thing he would do, since they all ended in a loss or stalemate for him. Undoing these encounters within the story doesn't make them non-canonical - instead, it solidifies them as having-once-happened.

• This may depend on the Toymaker's perspective on these events; manipulating the Doctor's wider history might be justified as making the game "interesting", but outright erasing his own past encounters with the Doctor might be perceived as 'cheating' as he's affecting his own history and creating the impression that he can't win in a fair contest. Since these other games all basically ended in a draw, the Toymaker can argue it's still one clear win to the Doctor and a series of games ended on technicalities, but now he's prepared to face the Doctor in a definitive game.

The bi-generation is essentially an inversion of the Watcher

When the two Doctors are talking in the TARDIS after the Toymaker's defeat, Fifteen observes that he's basically Fourteen having overcome the trauma of his last few lives, and even Donna refers to Fifteen as the future Doctor rather than the "other" Doctor. This seems to suggest that Fourteen will now just have a single life, and when he dies "again" Fifteen will somehow receive the full benefit of his memories, having already 'inherited' the emotional benefits to overcome Fourteen's trauma.

Fantasy foes

RTD has stated Fourteen invoking a superstition at the edge of the universe and therefore letting in myth has caused the show to take "a sly step towards fantasy", with Fifteen confirmed to face goblins. With that in mind, what else could future Doctors face?

• Genuine Egyptian gods, not the Osirans
• Genuine witches, not Carrionites
• The actual Odin, not the Mire leader
  • Could also be justified by the Toymaker's statement that his "Legions are coming." After all, the Toymaker is an Outside-Context Problem who does not conform to any of the rules of the Whoniverse. His Legions (or maybe "Toys") similarly don't need a sci-fi reason to exist, they just do.

The TARDIS has ALWAYS been wheelchair accessible.

The Doctor is just pointing it out because Shirley happened to be there.

Barney Stinson was actually the Toymaker ALL ALONG!

Hence his vagueness about his past and private life, his penchant for "magic" tricks, the various weird personas he adopts in order to seduce women, his warped values and his incredible competitiveness. In 2000s New York he is simply playing a twisted game with the lives of the other characters. He even remarks at one point "I accept your challenge".

The game that the Toymaker played with the Master was actually an entire season of RuPaul's Drag Race UK

Both the Master and the Toymaker showed great affinity for showing off, dancing and lip-syncing to music ("Rasputin" and "Spice Up Your Life", respectively), and the Toymaker has shown that linear time means nothing to them. The Toymaker and Master made it to the final, where Ru judged the Toymaker the winner. Which, considering the Toymaker is not allowed to cheat, meant that he had the Charisma, Uniqueness, Nerve and Talent to make it all the way through. Never one to be upstaged, the Master would've given it his all and despite his nature, would not have been able to backstab the other Queens (other than "throwing shade") because that would be "cheating" and the Toymaker would win. Or maybe he did cheat and that's why the Toymaker turned him into a gold tooth?

Others in the Toymaker's pantheon

RTD has stated the Toymaker is part of a pantheon and hinted that previous Eldritch Abominations the Doctor faced were part of this pantheon, and invited viewers to speculate. With that in mind:

• The Gods of Ragnarok, who Fifteen mentioned (which could act as Foreshadowing) and RTD name-dropped as an example
• The Great Intelligence, who is stated by the EU to be Yog-Sothoth
• Fenric
• Kronos
• The Solitract
• The Kasaavin
• The Timeless Child's species
• The Trickster (Maybe The Toymaker is also a member of the Pantheon Of Chaos?)
• As in the EU, the Toymaker is in fact the Crystal Guardian, and the "Pantheon" is actually the Guardians of Time.

The Doctor will wind up catching a ride with a Zingo in an upcoming episode.

• This will take place in Fifteen's own regeneration special, providing some nice Book Ends.

The One Who Waits will eventually turn out to be The Valeyard.

If you think about it, he is The Dreaded of the Doctor's many incarnations, to the point where Valeyard has been given a new moniker to hide his true identity, which would alert The Doctor if his true name was uttered. It would also make sense if Fourteenth Doctor eventually becomes Valeyard after many years have passed due to his rehab not working out, allowing the depression to consume him over time. Effectively, he would wait for the depression to takeover. Regardless, Valeyard taking on a hidden moniker would make sense.

Any Time Lord can bigenerate, it's just that the Time Lords were trying to stop it from happening.

Naturally any Time Lord has a chance, albeit a small one to experience a bi-generation given their time sensitive status. When they were in control, however, the rules of time that they enforced prevented it from occurring, limiting a future incarnation's interaction with their present self to some off-shoot like the Watcher or whatever the Valeyard was. Much like the Reapers or interdimensional travel the Time War unseating them from power has made space-time more flexible and a Reality Warper like the Toymaker finally triggered this occurrence. The ban was done either as a side-effect of other solid rules they established to time, or as one of those paradoxes they wanted to avoid as bi-generation allows the future incarnation to retain memories of the event when they normally wouldn't with a regular multi-incarnation crossover.