This is a "Wild Mass Guess" entry, where we pull out all the sanity stops on theorizing. The regular entry on this topic is elsewhere. Please see this programme note.
They Shook Hands
Harry is going to kill Voldemort only to take his place as the Dark Lord.
The plot was largely the same until the end of Y3, when things seem to break rather sharply. On the tin, Y4 is the same, but it is learned at the end that the plot went off the rails. How similar will Y5 be?
Year five will be completely different - with the political backing of the Malfoys and other well-known families, the wizarding world will accept that Voldemort is back. Perhaps this will mean a different teacher than Umbridge, or, Umbridge training them for war ala Hitlers Youth.
Confirmed: Umbridge forms a duelling club that is equal parts propaganda and training called the Ministry Youth.
Which of Harry's cohort in Slytherin will betray him? Some Slytherin parents will surely not be as brave as the Malfoys to turn their backs on the Dark Lord.
Theo and Harry's recent fallout is a red herring. He won't betray Harry - that would be too obvious - it will be someone really close to him, maybe one of the girls, and it will break Harry's heart.
The part about Theo not betraying Harry is confirmed. He ends up poisoning his own father to get out of being a Death Eater.
In book 5 Blaise Zabini comes back to Hogwarts. He is the perfect, if not very obvious, potential traitor.
Harry will befriend dwarves. (Just because Dethryl has mentioned several times on Potter Fic Weekly that he'd like to see it happen.)
Additionally, their friendship ends up being useless.
If Harry tries to learn Occlumency as he did in the canon, his friendlier relationship with Snape will mean he will actually learn it this time round.
Confirmed: Though Snape doesn't teach it any differently, Harry doesn't hate Snape and is therefore able to learn it.
Alternatively, Harry is just plain bad at Occlumency.
In the canon Draco had a small talent for Occlumency. Without Bellatrix to learn it from, he will take the lessons with Harry. They will engage in a friendly rivalry about it - making them strive harder and harder to be better at it.
Dethryl is being very sneaky about what the ships are in this fic. He doesn't talk about how it's going to develop, so there's a lot of speculation as a result.
Harry: Dethryl went out of his way to write Ginny into the story, so does that mean it'll be Harry/Ginny? He's dated Tracy and Padma, kissed Daphne, and is the crush-object of Laine Slater. Will Harry wind up with any of them? Harry/Pansy?
Draco: He's officially betrothed to Pansy, but they had an ugly breakup in Y4. He's professed interest in Parvati, but that may just be to get back at Pansy. Draco/Ginny? Draco/Daphne?
Draco/Astoria is a possibility. It is canon, and it would be interesting to see how Daphne would react to such a thing. However we haven't been properly introduced to Astoria in the TSH world yet, apart from a quick throwaway line.
Theo: Theo/Pansy is even more volatile and over-the-top than Ron/Hermione. They went to the Yule Ball together but had a miserable time.
Snape's love for Lily will with be a) learnt of the same way it was in cannon, b) learnt of sooner or c) Harry will never find out - maybe Snape will tell him he was friends with Lily but his friendship with Harry will mean he doesn't say anymore for some reason.
Harry's Animagus form: Is something that is small, furry, vaguely weasel like, and a predator. Harry is a mongoose. Which makes for some fun symbolism. Mongooses kill snakes.
It's not clear if Barty Crouch, Jr. was impersonating Moody, someone else, or even if he was there at all.
Deathly Hallows changed setting from Hogwarts to life on the lam. Will Dethryl do the same? Will Harry (and any companions) leave Hogwarts in Y7? Later? Earlier?