2. The Rings of Akhaten
In this episode of series 7, the Doctor takes his newest traveling companion Clara Oswald (Jenna Louise Coleman) to the Rings of Akhaten to observe a unique cultural and religious ceremony. It is believed that the songs contain the memories and stories of the past and that as long as the song never ends, the god known as Grandfather will not awaken and devour the universe. While briefly separated from the Doctor, Clara meets a little girl named Merry Gejelh, the Queen of Years, who is afraid of singing her part of the song for fear that she will make a mistake and awaken Grandfather. Clara convinces her that she will do just fine, and both she and the Doctor go to observe this part of the ceremony. Needless to say, despite Merry not messing up, Grandfather awakens.
When He Should Have Regenerated: The Doctor discovers that Grandfather is a giant parasite who feeds off of memories and emotions, and attempts to save the day by telling Grandfather a story of himself. He puts his entire history into the speech, hoping it will overload Grandfather due to how extensive it is, but he fails to do so. When Clara comes back with a token (a leaf that led to her parents meeting) that symbolizes all of her mother's lost potential by dying young, the leaf disintegrates and is absorbed, and the infinite potential history overloads Grandfather and he dies. What this, and the mythology of Grandfather, shows is that when the memories are absorbed, so is the person, or object, that contains them. When the Doctor failed to overload Grandfather, he should have either been absorbed, or he should have died and regenerated. Either way, he shouldn't have just slumped over weakly before Clara happened to save the day. It goes against the established mythos the episode presents.