YMMV / Portal: Prelude

• Continuity Snarl: At the end of the mod, Abby is able to attach the Morality Core to GLaDOS to stop the latter from killing everyone, a method proven to work in Portal. Here, though, she's able to do it anyway, even after the Core's attached.
• Nightmare Fuel: Take the Nothing Is Scarier-type eeriness of the normal series and make the test chambers ten times more complicated and harder, with walls that disintegrate you, many chambers that require you to work under pressure, and a much more powerful GLaDOS as the boss (this time, she has shockwaves, lasers, and telekinesis as attacks). If that's not bad enough, the game also goes into full-on Survival Horror mode towards the end when you're retrieving the Morality Core, where you have to venture through the dark hallways of the facility being pursued by Manhacks and security rockets.
  • The human overseers can easily count. They know just how deadly the test chambers are, since they designed the testing track themselves. Eric is lecherous and is giddy when he gets to kill you personally if you get stuck in one of his favorite test chambers, while Mike and Peter act way too nonchalant about how deadly the course really is. At one point, Mike and Peter talk about the various test subjects who got as far as you did - one died from bleeding out, and one of the other ones got decapitated near the very end. He describes the scene like another day at the office, and reminscenes about one of the new guys who got sick that day, before confusedly stating that he never saw him after that. Oh, and as a side note, from that conversation you can gleam that every test subject is a girl like Abby. No reason is ever given.
• Spiritual Successor: Several test chambers are identical to the layout of those to Portal: The Flash Version and its mappack mod version. Just with increased difficulty, of course.
• That One Level:
  • All the advanced chambers.
  • Test Chamber 09 requires precision and timing to get through, and good luck on that infinite loop. There's also an advanced chamber for that. There is an alternate route to the exit that takes you under the disintegrator, skipping the timing puzzle involving the Infinite Loop exit, but it requires just as much precise movement to pull off as the original method.
  • Test Chamber 18-19 is pretty difficult and requires a lot of good timing and difficult jumps. There's even an advanced chamber for 19, where the hallway portion is crammed full of turrets and rocket launchers and half of the platforms in the final part are metallic (which leads to a particularly tight, frustrating jump around halfway through). Good luck!