6. Little Nemo: Adventures In Slumberland (1989)
A joint venture between American and Japanese animators and based off William Randolph Heart's comic strip, it endured a long and troubled production. However, upon release it enjoyed some generally reviews, but lukewarm box office returns. The story follows the titular Little Nemo, who has bizarre and surreal dreams, but is eventually sucked into one of his dreams. It's everything he ever... well, dreamed of, until he accidentally unleashes an ancient secret that could destroy his dream and the real world itself. Were it to become a franchise, they certainly wouldn't lack for material. The comic strip that originated the character ran off and on from 1905 to 1927. Plus, what deeper well of stories can you summon than the mind of a child?