Remember back when there was a stigma attached to animation, where it was just a bunch of fluffy talking animals and it was only for kids? Yeah, I don't really, either. For the better part of my life, animation has been widely accepted for any age, in many different countries. But I still think we should shed some light on the smaller, darker, more mature ones, and remind ourselves that not every cartoon is from Pixar and Disney.
So here were my major rule for this one: the subject matter had to be mature and intense enough as to merit not being "for kids", even if a couple of them are still rated PG or PG-13. There's a lot of films that could've easily been included because of going into darker territories than most, like Antz, Fantasia, Spirited Away, Rango, or Iron Giant. But I feel that all of those are still aimed at children, despite clearly wanting to expand their minds a little bit. For the ones on this list, I really feel that almost no child would be able to sit through it all.
Final note: you may notice a lack of Ralph Bakshi here. He's kinda infamous for being the first dude to make animation very adult, with his films like Fritz the Cat and Heavy Metal. The only reason he's not here is simply because I haven't seen almost any of his flicks, except for Lord of the Rings (shudder) and half of Heavy Metal (yeeeeah, I just couldn't finish it). Anyhoo, here we go….