Bladegash is right, I want to end the run with beating Bowser (I think that every Mario run should end there), and therefore I count Bowser's Backdoor as level 97.
Today I did Castle#4.
In the first room, there are these 2 Ball-n-Chains before the door. I saw 2 possibilities to get past them: Either duck below the first one and then jump over the second one, or fly against the first one, which causes Mario to become invincible for a short time. Both methods were equally fast, but after talking about it in the IRC chat I chose the first one, because this is a lot harder (if not impossible...) to do in normal speed (I duck for only 5 frames), while the invincibility can be done quite easily.
In the second room I just flew over everything; hitting the Bony Beetles (yes I looked up the enemy names :P) would have pushed Mario into the spikes or flames...
In the third room I spent most of the time just jumping up; I only pressed UP for 1 frame each to climb on the fences, except at the beginning, where I needed some more height to jump over the edge.
In the fight against Ludwig I noticed something strange; when Ludwig does the following movement:
this causes Mario to stop abruptly for a few frames. I found no way how to prevent this, so I thought why not use this time to switch from feather to fireflower :) (as TNSe put it:
Ludwig never knew what hit him)
Unfortunately switching back to feather in mid-air would have caused Mario to fall down a bit slower (4 frames), that would have looked even cooler. But it's still my favourite boss fight so far :)
After I was done with Castle#4, Mazzic asked me to have another look at Vanilla Fortress, because I bumped into the ceiling quite often, which looked (and sounded!) quite ugly. I must admit I hadn't noticed this before, because I usually play without sound. He also told me about the A+DOWN trick, which causes Mario to just float in the water horizontally and not rise up too high (this is usefull to swim under enemies even in very narrow passages).
So, I redid Vanilla Fortress, entering the first pipe in the exact same time and entering the red door 7 frames faster (making use of the trick).
Now the Reznors were in a bit different positions, and I could hit the first and the second one a few frames faster. Unfortunately the second Reznor had spit out a flame before dying, and avoiding that flame slowed me down a bit, so in the end this fight was only 1 frame faster than the old one (so overall I was 8 frames faster than the old version at this point, and also needed 1 timeunit less).
Hexing Butter Bridge 1 into the new movie worked without problems, and I even won 1 frame in the fade-out sequence :). Butter Bridge 2 also worked without problems (after deleting this 1 frame), and then in the fade-in sequence to castle#4 I won another frame! (and then the castle also worked without problems)
So in the end redoing Vanilla Fortress gained me 10 frames :)
You can download the video from Vanilla Secret 2 to Castle#4
here
If nobody has any other objections to this, I'll hex it into the full movie tomorrow, and then stop working on this for a month.