Carnivore Confusion: When Kimba became the new king, all of the carnivores, including the titular character, weren't allowed to eat one other. They eventually decided to feast on insects.
In the 1993 dub and original Japanese, it's shown that Kimba struggles with allowing the carnivores to use the locusts as a food source, but it's that or the predators continuing to attempt to eat the other animals in the jungle. Even Kimba is not exempt from his natural urge, occasionally going wild with hunger (but stopping himself from actually doing the deed)
Later Inverted (or is it subverted?) when an artificial meat substitute is found
Cerebus Rollercoaster: As typical of Tezuka, the manga is filled with both idealism and humor while still pulling no punches when it comes to showing kids how cruel and uncompromising the world can be and as well as the cost, but also necessity, of self-sacrifice. The anime series? Not so much (due to Executive Meddling), but it still managed to sneak in a serious moment from time to time.
Darkest Africa: Both Played straight and subverted. The main chunk of story takes place in the last bit of frontier on an Africa on the fast track to becoming a world power. Kimba himself joins in by reorganizing the jungle along the lines of human civilization. In fact, a running theme of the story is the battle between this modernization and nature itself. It's a tie.
Darker and Edgier: The 1980's remake series. This is probably because Osamu Tezuka – gravely ill even during preproduction – had almost no input into the remake, dying after the sixth episode was completed. In the final episode in the Japanese version, half of the main cast, including those that didn't even die in the manga, just got shot after a whole freaking 52 episodes of them appearing regularly.
Downer Beginning: The series starts off with Kimba's mother being captured and his father being killed in the rescue attempt. Snowene lives long enough to give birth to her cub – but soon as he's old enough and been told about his father and heritage, the ship gets caught in a nasty storm, Kimba is urged to escape before it hits. He's swept away and wakes up among the debris of the ship. Kimba quickly realizes his mother did not survive the storm.
This caused some confusion when the localizers of the sequel series learned NBC's trademarks had lapsed, and attempted to go back to using the Japanese names. To try and justify it, they hinted that 'Kimba' may have been Leo's nickname when he was younger. This may have worked had a few characters not pronounced it 'Kye-mba'.
It also would have helped if dub Leo hadn't said that "Kimba" translated to "coward" in the language of animals, and was apparently called that when the other animals didn't trust him as a king. But to someone who has seen the original series and knows that his father chose that name, that makes no sense... ah screw it, it was the best the dubbers could come up with.
Downplayed in the case of Caesar in the Manga and original Japanese: while Caesar was a good king to his loyal subjects, he had little mercy for animals in captivity. Believing that in fact, animals that served humans were unfit to live and fair game for good eatin' – however in the dub this particular detail was generally omitted, and it was instead implied that Caesar was as progressive as his son. Though that makes some episodes somewhat awkward (like Sampson's return, who offers some former pack-mules to Kimba as an offering for a celebratory meal).
The Hero Dies: Kimba in all but the 60's TV series and the TV special. The 1989 series doesn't come out and say it but whatever happened, our hero's been shot and is currently bleeding to death....then there's a shot of the clouds.
The main reason why the Neo-Jungle isn't working in the TV special. Mixing species together turns out to be a bad idea. Turns out this was intentional. The Director had planned to use the mixed jungle to weed out the weaker animals and create new species. He kind of let this get to his head.
Mood Whiplash: The first episode. It literally goes from tragedy to comedy and back every minute or so.
Never Say "Die": The 60's dub. "I'm just going to lie down for a minute..."
Not So Different: While we have some humans that don't have any second thoughts about killing animals, we also have a few animals that are more than happy to lead humans, whether they're good or evil, to their deaths.
In Leo the Lion, this is what Totto tells Leo after he (supposedly) kills Mandy.
Pretty Butterflies: Kimba followed a swarm of migrating butterflies to get to land when he was lost at the ocean during the first episode.
Punny Name: The dub has its fun with Paulie Cracker, Speedy the Cheetah and the like. Kimba/Leo's kids are given this treatment in the manga... thanks to Paulie/Coco remembering the names mean to 'sleep' and to 'wake up'.
Bittersweet Ending: The Neo-Jungle is destroyed, the animals are left in the hands... er, paws... of a literal scaredy-cat emperor, and the real jungle has been blasted into all oblivion. At the same time, they now have a way to communicate with humans, a cure for the rampant plague that would have killed them, and a new-found drive and determination. We just never get to see what happens.
Cloning Blues: Toto. To the point where he's blinded by rage for all of humanity.
Jerk with a Heart of Gold: Applies to the monkeys. Sure, they pick on both Leo and Kenichi, but at the end of the day are more then willing to follow their emperor. And fight The Dragon and provide a bridge for Leo nearly sacrificing their lives.
Mythology Gag: At one point, Kenichi sees a flock of birds, very VERY similar to the original Jungle Emperor opening.
"World of Cardboard" Speech: Leo gets one towards the end. While the other animals think opposing the humans will be utterly useless, he decides he's had enough of being a crybaby.
Leo: My father was strong right? He was a real Jungle Emperor, right? But I'm different from Father. I'm small, weak, I'm afraid of heights, I'm really just a cowardly lion. But... Father said I was strong. That's why... That's why, I'm going!