Improvements:
2-3 Metaknight
http://dehacked.2y.net/microstorage.php/info/1121243949/2-3%20metaknight.fm2 (12 frames faster, not optimized)
entering 2-4
http://dehacked.2y.net/microstorage.php/info/1364854842/entering%202-4.fm2 (9 frames faster)
3-1
Wallclip is possible. I don't know if it's fast enough.
http://i.imgur.com/63l8NdR.png (Note: I have edited laser position to make this work but it should be doable without cheat)
I also don't know if this "get hit while hitting" clip works only on right walls or also on left walls. The original
twitch vod when the trick was discovered doesn't work anymore and I have only ever done this on right walls in my
1:54 TAS.
4-4
http://imgur.com/Pn2jPK0
In this room, I can stand in the spot where the clip is done about 10 frames faster by inhaling in the air. I don't know how to do the clip so I can't make a movie to tell if it really is faster.
http://i.imgur.com/0IwKOTM.png
At this spot, instead of falling down and spitting on the swordman, spit it away immediately and inhale the swordman. This saves 3 frames at least.
http://i.imgur.com/r9KgU5L.png
At this spot, you can slide and save about 7 frames.
5-2
http://i.imgur.com/t2ZmfAV.png
wallclip might be possible here and save a gazillion frames.
I can't get it to work though. The swordman stands too far away when slashing.
http://i.imgur.com/QCtR0AP.png
This spot looks promising. I can't get it to work right now, but we should investigate this. It could be a seconds timesaver.
5-5
http://i.imgur.com/pICnCWr.gif
This wallclip saves a few seconds.