The yellow room with five red blocks (there's a screenshot of it) is unreasonably difficult, unless there's some fifth secret I haven't yet figured out. Getting past the second and fifth red blocks, specifically, where you have to flip somewhere while you're in danger of getting hit to avoid falling into one of the two pits (or escape out of the pit, but that's significantly tighter on timing)
Also! The player's position isn't rounded to the nearest visual pixel for collision detection like it is for rendering, so it's almost as if you may die randomly if you look at the spikes wrong. This is actually "unfair" to the player, whose screen looks the same yet results in different outcomes, while the large player hitbox is simply "unforgiving", something the player has to get accustomed to, but it isn't unpredictable or impossible to account for.
While that yellow room is there, I don't know if I can get under ~12 deaths or get close enough to beat the 2:30 par time. Gotten S plenty of times, V is out of reach.