These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
That One Boss: The 2nd Dr. Bleed surgery. All the various hard-as-hell surgeries (which are usually made hard by Guide Dang It moments,) tend to be much easier once you know the trick behind them. The 2nd Dr. Bleed surgery, on the other hand, is a four-part Marathon Level against poison, fire, buried chunks of crystal, and finally a tapeworm that takes more hits from the battery to kill than the last tapeworm (and can quickly cause Bleed to...er...bleed out if you're not multitasking between cauterizing the cuts it makes and zapping it.) And you have just enough time to do it all quickly and flawlessly.
Napoleon Trotterski from the second game. It starts off easy enough, but suddenly ends with the player having to spell out words on a Speak 'N Spell. And if you aren't fast enough, the Speak 'N Spell suddenly explodes, leaving flames and burn marks that'll almost certainly obscure the screen and the keys, and if you try to put out the fire/heal the burn marks directly when they're on the keyboard, the game will assume you're hitting the keyboard instead and explode a second time. Not that you'll have any time to put out the fire anyway, because the words are coming faster and faster while you're trying to spell them out while not being able to see what the hell you're supposed to be spelling because the goddamn fire is in the way.
And if you thought that was bad, imagine trying to spell those words without knowing that you can use the computer keyboard to type them.
On the iOS version, the Mystery Boss in the second game requires you to tilt your device to move a flashlight around. And while you're doing this, there's a bee randomly flying around and only landing for a second in which you have to zap it. The difficult controls and the small time window combined make this unfairly difficult.
It's not any easier in the PC version. Poison builds up quickly, and while you're trying to clean up the poison in one area, it multiples in another. Meanwhile, that goddamn bee keeps stinging him. And every time you syringe out poison, it makes a small cut. If you lose track of them, the patient's heart rate will plummet.