Remus Lupin is really James Potter

Thoery: Remus Lupin and James Potter used a switching spell before Voldemort attacked, therefore Remus would then be dead, but in James' body. making James stuck in Remus' body. Confusing?

PROOF

FOR: Lupin really treats Harry as a son, rather than a student. He knew Harry before they introduced, and cared very much for him on the first day they met.

Multiple times in book five it would say Lupin shook everyone's hand, but "gave Harry a clap on the shoulder"(chapter.10), or, talked to Harry(chapter 24). Also, in chapter 35, he "grabbed Harry around the chest", consiquently stopping Harry from going to get Sirius from the veil and probably die, too.

AGAINST: If this is the correct version of THE GOBLET OF FIRE, then during Priori Incantatem, Lily comes out of Voldemort's wand and says "Your father is coming", though I heard that this was changed in later editions to James(Lupin) coming out first, and saying "Your mother is coming".
I personally don't really find this adequate proof, but some may.

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Dumbledore is an Animagus

Thoery: Professor Dumbledore is an Animagus.

PROOF

FOR:

"Dumbledore" means "Bumblebee" in old english.

Dumbledore always seems to know everything that is going on at Hogwarts.

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Harry is Gryffindor's heir

THOERY: Harry Potter is Gryffindor's heir

PROOF

Harry's parents' hideout was in Godrics Hollow.

Harry pulled Godric Gryffindor's sword out of the sorting hat in the Chamber of Secrets.

Harry is in Gryffindor


AGAINST:

The Sorting Hat wanted to put Harry in Slytherin.

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Harry is Slytherin's heir/descendant

PROOF

FOR:

Harry has Green eyes(J.K Rowling said that there was something special or magical about his eyes...)

The Sorting Hat wanted to put Harry in Slytherin very badly.

Harry has a special connection to Voldemort, who is the heir of Slytherin.

He is a Parselmouth (Though that might only be from the connection to Voldemort)

AGAINST:

Harry is in Gryffindor

Harry pulled Godric Gryffindor's sword out of the Sorting Hat in The Chamber Of Secrets.

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Professor Severus Snape is a Vampire

Thoery: Professor Snape is a full or part Vampire.

PROOF

I am going to put the proof for and against in the same section here.
First off, Snape can go in the sun, and Vampires typically can't. However, In J.K Rowling's world, maybe Vampires can go in the sun. Or maybe there is a spell or potion, like Wolfsbane, that allows him to be in the sun.

We have seen Snape eat at the staff table, which would suggest that he's not a vampire, assuming that he's eating real food. However, the house-elves may make special food for him(some type of Blood)

Yet another thing is that typically, Vampires repose, but don't truely sleep during the day, and are up all night. We don't ever see Snape reposing, but that doesn't mean he's not. We do, however, almost always see that he's up at night whenever Harry's wandering around at night.