This one definitely is fun. It's a silly but awesome dinosaur "documentary" that takes its subject very literally :)
"Dinosaurs: Terrible Lizards"
This one took me a little while to get. I watched this video once, and was kind of "meh" about it. In particular i didn't really like the extraneous intro and extro, and although the main joke was amusing it did start to drag a little partway through the video.
HOWEVER, then someone pointed out that there is a "translation" option in the subtitles. I can't say if it gives you a better appreciation if you watch it without the subtitles once first, but certainly if you get bored partway through restart the video and turn them on.
(Though in my case i had to turn the volume down the second time because i was having too hard a time reading the subtitles while the totally disjointed audio was going on, especially for Groot.)
"Hodor vs Groot Rap Battle"
I also have some reservations about this video. I don't actually like the song that much, but you've got to admire the amount of effort they clearly put into it. And of course i'm sure other people with different tastes in music might appreciate it a lot more than me.
"Dark Lord Funk - Harry Potter Parody of 'Uptown Funk'"