This game is really cutscene/loading screen loaded. Was funny when I watched back the entire run and noticed just how many cutscene skips and loading screens there are. They occur all the time continuously...
Also, the movement in this game is quite annoying for speedrunning because Harry has this kind of sliding motion and also the turning goes at random speeds. Sometimes the camera swooped around very quickly and sometimes it moved slowly. You'll see in the run that I don't always go around corners smoothly for example.
Thanks to Inexistence for a shortcut in the Spongify challenge, and for his support throughout basically the entire run so that I would actually get the run finished ;)

Some tricks:

I noticed that when you jump and wave your wand your hitbox will be a bit higher. Though it didn't have that much use in the run.
When you wave your wand and bounce off a bouncing pad you bounce a tad higher, causes a nice little shortcut in segment 37.
Also, when you bounce off a bouncing pad you'll get no fall damage which also created some nice shortcuts.

And now for some small comments about the segments (And also to show you where the segments are since that's most of the time not obvious in the video).

0:00:05 - Segment 1

Most epic segment. Consists only of loading screens and cutscene skip screens, no gameplay :)

0:00:18 - Segment 2

I'm triggering the first tree smacking thing a bit later so I can go under/through it, otherwise I couldn't make it and needed to wait. There's the first trick, jumping underneath it so you won't get smacked by it.
The cutscene trigger before the first savebook can be jumped over, but if I trigger the cutscene then I get warped forwards.
Same story for the second tree smacking thing, I trigger it a bit later so I can go through it instead of waiting for it. Unfortunately it wasn't possible for the third tree smacking thing so I just trigger it and then wait.
The shot at the Gargoyle around the corner was lightning fast, so fast that it surprised me and made me skip the cutscene a tad too late (Stupid me for not holding the cutscene skip key pressed already... A couple of frames lost).

0:01:36 - Segment 3

Just some running from point A to B. I always giggle when Harry bumps against the front door. Not much else to say about this segment.

0:02:23 - Segment 4

The race is on! Harry versus Hermione and Ron. Hermione gets quickly confused and starts to run around in circles, Ron takes the lead, Harry comes in second. And we're past the first corner. Harry plays dirty and blocks Ron from moving forwards causing Ron to bump against the pillar, now Harry takes the lead and reaches the door first!
Unfortunately I couldn't skip the ghost cutscene, would've saved some seconds.
Those lessons you get in this game are painfully boring, and easy. Although it sometimes happened that the game registered a keypress twice resulting in failure...

0:04:48 - Segment 5

I fucking hate these "shoot enemy in some place" parts... Whichever moron invented that should be shot. Well, I guess for normal play it isn't too bad, but for speedrunning it often sucked to do it optimally.
The jump on the snail could've been avoided, I'm not sure why I did it actually although sometimes you can get a tiny boost from jumping on an enemy and bouncing off.

0:07:38 - Segment 6

I made this a separate segment because those crabs can quite easily have issues landing on the bottom part.
I didn't shoot the fourth crab before the cutscene skip because then the crab would need to be shot again.

0:08:17 - Segment 7

There was no way without slowing down a lot to skip the bonus bean part.
The Quidditch in this game is also extremely lame. You chase/catch up on the snitch automatically. You actually don't have to do anything besides actually grabbing it and dealing with the other team a bit (Let's get ready to rrrummmble!)...
It's awesome how Harry grabs the snitch even though the snitch is still quite a bit farther away.

0:10:51 - Segment 8

The race is on! Harry versus Hermione. Hermione blasts off and keeps her distance. Harry then cuts off a part by jumping off the staircase and catches up nicely. Though Hermione, with her power shoes, automagically runs faster than Harry (Hey that's not fair!). Harry has some huge difficulties getting past Hermione, even by using some fast cornering. In the end, Hermione remains victorious (It's them evil power shoes!).
You can touch the cauldron immediately except that the game will freeze up if you do. In the run I touched the cauldron at the exact right moment, frame perfect.

0:11:37 - Segment 9

The race is on! It's Harry versus Hermione again. But this time the location is familiar and therefore Harry remembered the dirty trick he used against Ron previously, so now he applies it again but against Hermione instead. It's an effective method. Harry wins!
But...! Oh no! Hermione magically teleported up the moving staircases. She should be disqualified! The race continues. Running past the corner they stumble upon Filch! Who tries to block them both. He almost succeeded blocking Hermione but both of our runners get past him nicely. Harry does some more corner cutting while Hermione takes the long road. And behold... Harry wins once again!
And as a reward Harry gets to do one of them boring lessons... (Why does Harry always needs to do these things? What about the other students?).

0:14:03 - Segment 10

I couldn't find any way of getting over those lower wall parts and dropping down right away onto the star :(

0:14:26 - Segment 11

That's a pretty fast Peeves fight ;) You can already hit him before (Or actually during) the cutscene.

0:14:48 - Segment 12

The next part was pretty tricky to do so I made it a separate segment. It's a neat trick.
Also, I like it that you can jump on the snail platforms to activate them :)
And the last trick with the pendulum (Or how is that thing called?) is also neat. I'm skipping the trigger that lowers it by jumping around it and on the side of the platform.

0:16:09 - Segment 13

The race is on! Harry versus Some Dude (I'm not sure who it is, one of those twin brothers I think). Some corner cutting and precise movement leaves Some Dude in the dust. Even his power shoes (Yes, he has them too!) won't help him anything. Harry wins!

0:16:50 - Segment 14

Not much to say about this one. And whichever moron invented those "shoot enemy in some place" parts should be shot... That was terrible in this segment.

0:18:19 - Segment 15

The trick at the big dropdown is to press forward again right after the cutscene, otherwise you'll fall straight down and die.

0:18:48 - Segment 16

A separate segment for a tricky part (That, and the savebook was on the way). Could've shot the lock a bit faster though so that in the next segment I wouldn't need to wait a bit.

0:19:03 - Segment 17

Not much to say about this, pretty straightforward.

0:19:39 - Segment 18

And in this segment you'll see a very fast duel :) Even Snape can't finish his "begin duel" sentence.
The trick to hit Malfoy is to shoot and just before it hits move to the side. Not all too easy to do as it needs to be timed right, but it wasn't all too hard either. 2 full charged blasts will finish him off.

0:20:27 - Segment 19

The race is on! Harry versus Ron. Ron steers away quickly and evades the guy nicely. But Harry stays on Ron's tail. A corner cut on the staircase brings Harry in the lead, but Ron's power shoes kick in and he still finishes first...
But the race isn't over yet! The outside will now be the playground of our runners. Ron gets a head start (Grumble!) and so Harry needs to give all he can to win from Ron. Can Harry win? Or will Ron remain the fastest?
First a 100m sprint where Ron's power shoes come in good use. As Ron gains more and more distance (He even waits and taunts Harry, the bastard!), Harry cuts a corner again and draws near to Ron. Some more precise movement and corner cutting will draw him ever near, but alas... Ron still wins.
As a second place reward, Harry gets one of them boring lessons again...

0:22:32 - Segment 20

You can't use the third snail on the outside part because the ledges are too high and you can't get the snail on it.

0:23:08 - Segment 21

An unskippable cutscene, I've seen that one so many times...
About the part where you need to push the block on the little platform/elevator-like thing, you can also stand on this elevator and jump off to keep the gate open but it only works when you've skipped the cutscene first.

0:23:58 - Segment 22

Pixies are horrible creatures, they can hit you very easily.

0:24:41 - Segment 23

This was an annoying segment to do over and over. In the part with the snails where I push the snail against the other one, I'm not losing time because it still requires the same amount of pushes. It doesn't look too pretty though :)
I really hate these "shoot enemy in some place" parts...
By the way, grabbing both of the stars in this challenge makes no difference anymore, Slytherin has too many points at this time so I can't get the bonus bean part anymore.
Oh, and did I already mention that I fucking hate these "shoot enemy in some place" parts?! They just thought up something mindless for the player to do to waste time as it's not exactly hard to do...

0:27:07 - Segment 24

I love the 180 degree turn, perfectly executed :)
But not to forget, the race is on! Harry versus Ron. Due to the quick 180 turn, Harry goes side by side with Ron. But due to Ron's power shoes he starts to gain more distance. Until Harry does some corner cutting again (By the way, fun fact, in an earlier segment when I needed to get past this part I ran on the right side of the tree around the corner. While now I run on the left side of the tree, heh :) I noticed this after rewatching the entire run.), so that Harry closes in some more.
But it seems that Ron has added some nitro in his shoes because he spurts away so quickly again! Apparently Harry just can't get past Ron! Is all lost? Is the battle already decided?
We're entering the garden house now and Ron still leads. But ooohhh, what's this? Harry seems to have found a shortcut! Ron, completely unaware, takes the intended path while Harry takes a table trip and slips by Ron by a nose length! Now even his power shoes (Combined with nitro) can't save Ron anymore. The battle is over, Harry wins!

0:27:45 - Segment 25

This segment contains a pretty awesome shortcut. Required quite some luck manipulation to get done because the Horklump Mushroom can fall randomly in any direction. Not to mention that everything else needs to go correctly as well.
And in this segment I lose my health potion, stupid prickly plant ;)
And at the end of the segment it appeared that you can just jump into the house instead of pushing the button to create a bridge...

0:28:42 - Segment 26

The race is on! Harry versus Some Random Dude. As always the opponent(s) gets a head start. But due to some corner cutting again Harry leads on and wins once again by quite a large margin!

0:28:59 - Segment 27

This segment contains a quite massive sequence break (About 3 minutes saved) because of skipping the whole Dumbledore part (Which contains a couple of unskippable cutscenes) by jumping past the ghost trigger. It's funny that the ghost will remain in that place for the rest of the game but the trigger will be gone.

0:30:08 - Segment 28

I hate those round staircases... Always annoying to do it optimally. When you restart a lot you get quite dizzy from it.
It's funny later on that you can just fall (Or jump) down and not get hurt, that only happens in this one place, no idea why.

0:30:36 - Segment 29

I restarted this segment as much as needed so that the big crab would fall to the right so I could just continue forwards.
Love them gnome guys, they're awesome, just listen to them :D
I could've maybe jumped through the window from the elevator part, should be a tad faster.

0:31:29 - Segment 30

Skurg... ugh, skurg... ugh, skurg... ugh, skurge!

0:32:00 - Segment 31

Not much to say about this one, nice "edge land and jump" on the hay though.

0:32:51 - Segment 32

A segment with lots of walking as the ever-growing-fatter-guy(TM). I like the song that plays when you're this guy.

0:34:34 - Segment 33

The part after the first little elevator is a little messed. The aiming there is odd because of some invisible wall thingy, I'm not sure how to explain. Anyway, so I kept restarting till I would hit the rope right away.

0:35:13 - Segment 34

Very tricky shortcut up ahead, the jump from the bridge to the other side. You can just barely make it and caused a good number of restarts... And of course everything else needed to go correctly as well.
The savebook near the end of this segment was not used for a new segment, the reason is because that savebook is bugged. If I would load the game there the screen would stay black which isn't very convenient :) So I didn't use it.
Dodging the last guy at the end of this segment was nicely done, I just barely avoid him :)

0:36:35 - Segment 35

The race is on! Harry versus Hermione. Hermione leads on and does not get confused in this part this time. Though she hasn't learned from the last time and Harry uses the push-to-pillar trick again. After some clever staircase jumping (You can still see the ghost there) the two runners meet again, except that Harry took a quick staircase shortcut although Hermione noticed it quickly and started running so Harry just barely got into the lead. Harry wins!
As a reward, boring lesson time.

0:39:05 - Segment 36

Not much to say about this short bouncy segment.

0:39:28 - Segment 37

Nice trick here, by waving the wand makes you bounce a bit higher so that you can barely grab the ledge. Shot an evil gnome to boot!
The part with the bouncer and the 2 buttons to shoot, if you shoot one you'll drop straight down so it needed to be timed right to land on the plank. And I also wanted to shoot the second button in the jump before grabbing the next plank which wasn't too simple either.
And then a shortcut at the end of the segment, as you can see it's possible to almost land on the platform without climbing up, but thankfully that's not possible otherwise I would lose some health (Possibly die...).
Was a pretty tricky segment to get done.

0:40:19 - Segment 38

Here's the shortcut that Inexistence found and it chops off a large amount of time. Just getting straight to the end instead of the huge route around.

0:40:30 - Segment 39

The race is on, and such. Ron wins though.
Not much else to say, just another piece of walking.

0:42:32 - Segment 40

On to the Forbidden Forest! The beginning here was annoying as I needed to turn around quickly and precisely and I had to block Ron otherwise he would block me. The "walking against Ron" on the outside in the tunnel was done so that Ron would be a bit slower and then later on, as you can see in the run, he would just barely not block me away and I can move straight to the cutscene trigger.

0:43:28 - Segment 41

The Forbidden Forest... Did the whole thing in 1 segment and it wasn't easy. Unfortunately there's a lag in the tunnel with the spiders, but besides that everything went great. I also luck manipulated the chocolate frog in the beginning so that I could grab it without losing time.
You can also see the first bounce trick here, bouncing off and then landing all the way down without getting damaged.

0:45:09 - Segment 42

The Aragog battle. First some quick getting rid of the web stuff (Though that one webpillar looks a bit messy, but I'm not losing much time, a few frames maybe, and the battle with Aragog was very fast in this attempt).
The trick in the battle is actually to stay close to him. And if you stay close and move around he'll get interrupted quite easily.

0:46:13 - Segment 43

Some staircase climbing again... (Haven't we seen those things enough by now?)
On to the Chamber of Secrets!

0:46:57 - Segment 44

A very nice bounce and drop trick here. Don't need no slow elevator ride!

0:47:10 - Segment 45

The trick here was to shoot the Skurge goo and then walk and climb up on the ledge instead of a jump and climb up. Because of the cutscene skip you'll get onto the ledge automatically and this speeds you up just enough to get through the 3 blades part (Hell, I even needed to wait at the last blade, that's how fast I was :P).
Shooting the rock? I ain't feeling like shooting some rock, I'll just climb up here thank you.

0:47:54 - Segment 46

This is a short and awesome segment!

0:48:14 - Segment 47

Those 4 assblaster turtles in the beginning were very annoying as they're both great and crappy at aiming...
Also used a jump and wave wand to get a faster climb up (Otherwise the climb up is like 1 second slower), I'll just point this out since it's not very obvious :)

0:49:01 - Segment 48

Great shortcut/trick here in the beginning, saves dealing with some damn pixies and button shooting.
In the Indiana Jones part, did you know that you can walk on some invisible ledge on the left wall and then skip the trigger for the fixed camera and ball that chases you? Then you can just go through this part normally :) It wasn't faster though, unfortunately. I also jump and then hold backwards/down to trigger the trigger a tad sooner.
And in the last part of this segment it wasn't possible to get through the wall at the first swing :( You'll always die or get pushed out of that place.

0:50:03 - Segment 49

You can just walk through the first 3 fire beams without getting hit. I needed to stop a moment at the last beam otherwise I would die. Perhaps if I didn't get hit by the 2 turtles previously I could make it through, I'm not sure actually.

0:50:18 - Segment 50

The final boss battle! A very random battle it is, especially the way I do it with all the goo flying around. It's funny how you can hit him before he gets out of a grate, then he gets all pissed off :) Battle went great. Look at all the goo on the floor! One hit and I'm toast. The last hit on the boss was a pretty lucky one because I was standing so close to him that he could easily hit me.

0:51:28 - Segment 51

And now a short last walking part to the ceremony to celebrate it all (Hermione got confused again...). It's funny how Gryffindor wins the House Cup even though they end up on the last place. Not to mention that Dumbledore says Ravenclaw ends on fourth place but the statistics say they end up on the second place. It's all a bit odd ;)

Final stats:

1 Wiggentree Bark
190 Beans

Rictusempra Challenge: 2499/4130
Skurge Challenge: 1885/3755
Diffindo Challenge: 1641/3927
Spongify Challenge: 1524/2750

Gryffindor: 402 House Points
Hufflepuff: 495 House Points
Ravenclaw: 506 House Points
Slytherin: 709 House Points