Getting sub 3 is really hard to do in 50FPS for sure as the timing is so tight but alas it's still possible.
optimal setup is snake, nemesis and super missile launcher, as well as a life pot.
The core thing to do is in B1, use your super missile launcher to level up at all the exp tanks.
In B2 there's not much to say except to pray to RNGesus and hope you only burn 5 or 10 health and lose 2 or 3 seconds to the shenanigans.
B3 you can get pretty consistent at though Movement and abusing the snake to hit delets through walls is very important, like right here
at both spots 1 and 2 you can fire a lvl 1 snake through the floor to set off the delets
everybody knows you can eat 10 damage and slip through here:
A really cool trick is actually the last 2 delets before heavy press
If you go right up to the delet and turn your back to it curly on your back will actually shoot through it and hit the second delet so you can set off both of them simultaneously saving 5 seconds of time! also yeah if you get damaged before heavy press smashes the floor you can enter sooner because you don't have to wait for him to go by because of your iframes.
As for the bosses, get good at mashing.
Your highest DPS is both you and curly firing the nemesis upwards while standing on the ground. This applies to both Heavy press (just stand there and take the damage by the rollers, the nemesis won't level down and has the highest DPS anyway) And Ballos 1.
Follow Ballos' movements while standing inside of him, if you mash fast enough you should only eat about 36 damage, and depending on how well you did in hell you'll want to eat your life pot either before or after this part of the fight.
Phase 2 is pretty straight forward, get in his eye and when he jumps, at the apex just hold left or right to fall back into place, easy.
Phase 3 is hard to one cycle, but possible, you want to end phase 2 on the right side of the arena so you have the max amount of time to finish off the eyes before he goes around to the top.
You can kill him closer to the left, but it's harder to finish off the eyes before cycle 1 is done, and if you miss the cycle that another 10 seconds lost and you're most likely not going to get >3 min run.
You can use super missiles in a clutch situation, but I don't actually remember how many missiles for either level 2 or 3 takes to finish off phase 4 as I never did the missile strats while attempting runs.
Phase 4 of course is pretty easy, just get damaged by the spikes on the floor and hop into one of his eyes and mash really fast with the super missile launcher to kill him.