I'll do these in chronological order because the run is pretty short.

1. Make sure to hold 'K' (or whatever you jump with) during cutscenes to speed up dialogue, mashing 'J' is usually slightly worse than having the timing down for all the dialogue boxes

2. You can jump on platforms while moving through them as long as your momentum is downwards: This saves a second or two in world 1

3. Ladder movement is important, you want to stay as high as possible on the first ladder while getting far enough right to be walking when you come off it. Second ladder you should only get on for an instant and walk on the top of it. Third ladder is just a door, you can press up to enter it immediately. And the last ladder make sure to come down it a platform size to be able to jump off it.

4. Swimming is all about timing the first down press, hit it after you touch the water then mash down until you're low enough. I just mash 'W' and 'K' after that, ideally you will break the surface and gain some precious forward momentum.

5. If you're fast enough in the water you can land before the (brain slug?) gets over and take a hit on him while holding right.

6. Make sure to jump hugging the wall before the first electric fence so you take another hit on a brain slug

7. If you miss the first brain slug you have to wait for the flying saucer at the entrance to the death warp room so you can 1-cycle it, otherwise head on in using the platform jump to save a few more frames

8. Mash jump and hold left to get the fastest jump coming in and you should be able to make the 1-cycle

9. Falling on the monitor so your foot just barely clips it will give you the maximum time to react and start holding right, which is necessary to get the fastest ladder drop cycle and avoid getting electrocuted!

10. Try to damage boost on the little green guy and land in the spikes to activate spike immunity (not technically necessary, think it's only actually a timesave in 100%)

11. When you're falling press left for just a tiny bit to move slower to the left and stay falling for more time

12. A frame perfect jump after the monitor can save a little time, but you can always just press left after falling for a very small amount of time and continue right for a safer route (I think it saves at most 8 frames? Definitely TAS-worthy)

13. Again, reach the max height of your jump before grabbing the ladder

14. Mash jump twice at the start of the next room holding right, then hold left as soon as you start falling. Jump between the two spikes and fall left slowly until you're past the vertical line of the lowest spikes. When you get below them hold right.

15. You can reach the exit to the ice room from the bottom platform if you time it right (gotta press jump very late and hold left to slow your momentum and keep holding jump)

16. Frame perfect jump in the final (mistake-possible) room coming out where there's a ceiling above you can let you completely hold forward the whole room

Think that's it, all my secrets to get a sub 3:50, I think that last one and #12 are the only ones I didn't implement in my WR. Besides that you can still definitely save a second on my run from better movement in a few areas and my dialogue wasn't particularly good in that run either. Thanks for reading, and good luck!

(might edit this to include videos if people want that, otherwise you're on your own kid)