Wow, Melon. Reading some of the comments on this post surprised me. I'm amazed people's introductions to any kind of cartoon MV's are PMV's! It made me realize I'm in that age group who was exposed to AMV's a few years before MLP came out.
My favorites were the Naruto Sasuke Numb by Linkin Park one and the "This is Halloween" Soul Eater AMV. I also made my own Soul Eater AMV set to "Dinosaur" by Ke$ha (back when she still had the Dollar Sign and that monster of a Producer) and I submitted it to the Megacon AMV Inferno in 2012! I made a few other lyric videos and AMV's and meme videos for personal enjoyment.
Me and my friends were mega weebs (short for "Weeaboo", a nonsense term that a certain notorious web forum arbitrarily replaced the slur for "Wannabe Japanese" with that then took on a similar connotation as Otaku). We even did the dances to "Motteke! Sailor Fuku" and "Bad Apple!" at a school festival as part of the club performances section. I went to American High School, complete with Emo and Swag kids and Twilight and Justin Bieber fangirls. Nobody understood what the heck we were doing or what we were cosplaying at that time! They just thought we were weird. I also made an actual music video for a school project set to the Vocaloid song Matryoshka that is buried away in my hard drive.
I was already on the cosplay scene with the Hetalia fandom when the MLP, Adventure Time, and Homestuck all had a rapid surge in growth. From 2011 to 2012 was like night and day at the huge conventions. One event, those fandoms were not noticeable, and the next year the cons were FLOODED with cosplayers from those fandoms. Pony art flooded DeviantArt with pony versions of characters for EVERY fandom. Pony.mov and the PMV's appeared. It was a great and fun and fascinating time to live through, and social media was in it's full heyday. I have so many stories from that time, it was something else!