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.
In fairness, though, spoilericity is definitely hampered by a severe lack of context in almost all cases, the only real exceptions being the pretty blatant deaths.
Seasonal Rot: AMV Minis Challenge #8 was to make clips using or inspired by Ylvis' "The Fox". Some creators took the assignment straight, some made fun of it and some even hung lampshades, but regardless the fans didn't take the episode well. It got nearly twice as many dislikes as likes on YouTube! The winning entry of the next challenge (Original Audio) was someone apologizing for Challenge #8.
Not helping was two factors: 1) The popularity of "The Fox" spiked quickly and then collapsed, meaning the challenge was based around a meme nobody cares about anymore, and 2) almost every clip used the same 30 seconds of the song, which got old fast.
Shout-Out: Griffith's fondness for singing show tunes in the earlier videos is a reference to the Berserk English dub outtakes, where Griffith's VA was a former Broadway singer. He started to sing sometimes if he forgot or flubbed a line (or just felt like doing so).
Squick: Pretty much the entire point of AMV Hell 0 and AMV Hell Divided By 0. There's a reason those two come with a huge content disclaimer.
Watch It for the Meme: If your first exposure to a certain anime is a spoilery, often gore-filled scene in AMV Hell, it can be fun picking up the series and seeing just how it gets to that point in the first place.
The Weird Al Effect: For everyone who goes about watching an anime series and goes "Hey, I recognize that footage from AMV Hell." or hears a song somewhere and goes "Hey, I recognize that song from AMV Hell." Even worse when it makes you remember footage from 0 or /0.