10 Huge Doctor Who Plot Holes Everyone Overlooks

After being shot by a Dalek, the Tenth Doctor begins to regenerate. Fortunately, he's able to divert his regeneration energy into his spare hand (Sycorax, Christmas, that whole thing) to avoid changing his appearance.

The side effect of this little trick was that he accidentally created a second version of himself when Donna touched the hand, fusing Time Lord and human DNA together.

The Metacrisis Doctor.

After the good guys save the day, the Metacrisis Doctor reveals his true colours and destroys the Daleks. This is an act of genocide and it deeply troubles the original Doctor. You know, as it should.

Ten leaves his doppelgänger with Rose, instructing her to make him a better man, just like she did for him. But it's also revealed that this version of the Doctor has the same thoughts, feelings, and memories as the original - so surely he already knows how to be better?

Granted, the idea of Rose "saving" this version of the Doctor - after the original saved her so many times - is sweet. But it also comes off as forced, since the Metacrisis Doctor should be fully capable of changing all on his own.