I don't know if somebody discovered that before but i don't care, i'm still gonna explain how did i discovered that.

Everybody knows that when you just hold space you perform a high jump, But while messing around level 12 i actually discovered something, when you hold space and w key you can actually jump a little bit higher???

https://imgur.com/a/Qfic01C - nonprofessional jump comparison

I have no idea how that works but somehow you can jump higher lol, anyways with this discovery you can actually do level 12 without double jumping and you can skip down stairs in level 15.