So, as the question says, what parts of the game have you had the most difficulty on (Circular Saws, Repelling circles, Falling Keys, etc)?
 
For me, it been a more general "whenever the game play gets loose:.  I have issues when I'm not running at full speed and bouncing off walls.

After spending an hour trying to unlock that dude from 'I wanna be the guy' I'm going to say spiked mother fucking walls.

Those fucking slow moving red blob cunts.

Saw blades that move up and down on walls. And you have to walljump over them :C

I've died so many times on so many types of obstacles so I'll just go with everything.

" I've died so many times on so many types of obstacles so I'll just go with everything. "

I've definitely had the most trouble with those asshole heat seeking bug things that explode into more bug things that also kill you.

" I've definitely had the most trouble with those asshole heat seeking bug things that explode into more bug things that also kill you. "

The X-Button .. I keep holding it even though it makes me run too fast and jump too far but I can't seem to be physically able to get my damn thumb off of that damn button.

" The X-Button .. I keep holding it even though it makes me run too fast and jump too far but I can't seem to be physically able to get my damn thumb off of that damn button. "

I would definitely have to go with the disintegrating walls. I'll be damned if I ever get the 2 bandages in that hospital warp zone.

" @TheWadeBrigade said:

" I've definitely had the most trouble with those asshole heat seeking bug things that explode into more bug things that also kill you. "

Yeah, those are nasty. "

Easily the demon missiles. The couple levels in Cotton Alley that have them in it make me so infuriated. Other than that, there isn't much that you can't do by muscle memory given enough tries.

the black hell mouths followed closely by the missiles

I really hate the super narrow corridor (that's one block high) where you have to jump over saws. The timing to get past that shit is so fucking exact I nearly screw it up every single time. There are only a few levels that I consider Holy-Shit-Nightmarish-Scarringly-Hard and that last level on Cotton Alley "Four Letter Word" is one of them. The very last segment where you have to squeeze through the narrow parts and jump over moving saw blades...
 
Oh, those Meat Seeking Missiles are dicks too. Hell Mouth Missiles are frustrating, I don't know if I hate it as much as the narrow corridor jumps though.

jumps that require a lot of finesse.

I found the gravity orbs (repelling circles) to be tough. Trying to get the perfect balance and fall speed was a pretty big hassle to me.
 
Still, fun game.

The part where there's these bandages, y'know...
 
 
:(

Fans seem to always piss me off, They just never seem work how I think they should.

" I've definitely had the most trouble with those asshole heat seeking bug things that explode into more bug things that also kill you. "

Air propellers.  Takes a lot of tries to get the "feel" of them and jump off of them properly.

" The black hell mouth things, because they are the only thing in the game that seem at least a bit random, which makes them hugely annoying. "

" Those fucking slow moving red blob cunts. "

Jumping through tight spaces.

The Chapter 5 - Light World Warpzone - Skyscraper.
Getting all the Bandages there was the last thing i had to do, and it took me 3 day with 2-3 hours per day. That one was even more messed up than the "I wanna be the Guy" - Warpzone cause it was so long and you had to restart all over if you mess up 3 times, so you first have to get to the tough parts to train them...