Ferngully is a region of the Australian rainforest inhabited by fairies, and one of them is Chrysta (voiced by Samantha Mathis) who today is receiving a history lesson from the wise, old Magi Lune (Grace Zabriskie) on how fairy folk and humans used to co-exist until the evil entity known as the Hexxus (Tim Curry) intervened and drove humanity away. But Chrysta isn't interested in those old stories, she wants to have fun flying around the trees with her friend Pips (Christian Slater) and the others of her kind, though she makes a mistake: she breaks through the canopy to see the world beyond. She has never viewed anything like it, but notes the sky, the mountain in the distance - and the cloud of smoke rising ominously from the trees.
When Disney's Aladdin was released the same year as this was, everyone was so bowled over by Robin Williams' vocal performance as the Genie that they quickly forgot he had been in Ferngully as well, probably because he wasn't as accomplished here. That said, if he had not opted to voice a wacky cartoon bat for which the director Bill Kroyer had obviously allowed him to improvise dialogue with, who knows if Genie would have been quite as successful as he was, as Williams work in the previous film sounded like a dry run for his tour de force later that year (actually Ferngully had been completed in 1991, but held over for a few months, seeking a better chance at finding an audience).
This being the nineties, one of the buzzwords here was "ecology" as it became increasingly clear, even more than it had been in the seventies when the movement truly established itself, that saving the planet had gone mainstream. In that previous decade quite a lot of the pop culture interpretation of what appeared to be a looming crisis was channelled into horror movies and science fiction thrillers, but things were a lot more touchy-feely twenty years later so improving stuff like Ferngully was the result, and though more reactionary voices were resistant it did have its heart in the right place and made its younger viewers target audience aware of the importance of being nice to the planet's flora and fauna.
This production garnered interest anew when it was claimed James Cameron's Avatar, which had become the most successful movie of all time (not accounting for inflation), was accused of lifting its whole plot from it, and it's true there are curious similarities, the amount of budget thrown at each of them recognised as somewhat different. There is a human character, Zak (former child star Jonathan Ward) who is supposed to be on the side of destroying the rainforest for profit only to be turned Chrysta-sized when she zaps him with fairy dust to save him from the machine which chops up the trees into planks. He accompanies her back to her home to meet with the Magi who can turn him back to his normal dimensions, but Batty the bat insists on warning her and the others that humans are bad news: they experimented on him, after all, hence his pixilated demeanour.
Along with Williams, who seems like a perfect choice for a cartoon now though didn't so much back then, there are some odd voices to be heard here such as Cheech Marin and Tommy Chong and briefly popular rapper Tone Loc as a hungry lizard (Williams raps as well, to a Thomas Dolby tune), though the attraction second only to the bat was Tim Curry, relishing the villainy of his gooey, smokey monster the machinery frees from the tree he was entombed within for centuries. The Hexxus promptly possesses the felling vehicle, sucking up its pollution like there's no tomorrow, and there may not be if he gets his way, so you can understand this was less than subtle and tends to live on in the hearts of those who grew up with it rather than animation historians and buffs. It actually resembled a far more wholesome Ralph Bakshi cartoon with its social concerns and character designs, if not its sense of humour, which grew more earnest the further the tale unfolded. Although few would call it classic, it did spin its modest charms and maybe made a beneficial difference. Music by Alan Silvestri.