Ok, there are lots of bad guys in LBT. Some more menacing than others.
Personally, my favorite villain so far is Sierra. I'm not sure if he's a Sharptooth or a Leaf Eater as he has teeth and looks more Sharptoothish but he isn't trying to eat any of the Gang of Five, though perhaps that's why he tried to snap at Ducky.
He is just plain evil. He and Ozzy, my third favorite, my second being the infamous Sharptooth from the first film, are just psychopaths who wanna kill others who get in their way. It's not even so they can eat, they just wanna get even and seem to hate the world and, in Sierra's case, are power hungry.
Sierra even looks evil. Heck, Ozzy and Sierra working together would be the Dangerous Duo! :!
As for future villains, I have an idea for some of those.
1.) An evil female Sharptooth Pteradactylus named Agatha who married a leaf eater (Pteranodon) that she originally loved, but began to hate when their hybrid son started to like him more than her and she and the father weren't working too well together and she feared he'd take her boy and leave. So she goes and murders and eats her mate in the dead of night. She then, to get her son to hate Leaf Eaters, saying they murdered his father just because he was a Sharptooth (no, he's not, but she'd a liar) and they took the body too. Her son would by the lie for years, and, eventually, getting tired of his overbearing mother, her son would leave and come to the Great Valley and befriend the Gang of Five. Eventually, she comes and tries to get him. When her son, deciding that she was wrong about Leaf Eaters being bad, decides that he's staying, she would reveal the truth that she indeed killed his father. She would threaten to eat the Gang of Five unless her son came. Eventually, the grownups would come and a fight would break out. Near the end of the fight, she would actually try and murder her own son, deciding that she couldn't turn him to her way of thinking, but would be knocked out by Petrie and Mama Flyer and would fall into a tar pit and die and her son would be adopted into Petrie's family.
2.) Evil three horn villains. Perhaps one that is an enemy of Cera's Grandfather and the bad guy's two sons, who would be childhood enemies of Topps.
3.) An evil Gang of Four that would try and get Littlefoot to join it and try and get some fabled Fire Rock (actually a huge lava rock) that is under the Great Valley and would, according to longneck legend, give the users of it great knowledge, which they hope to use to make themselves smarter than and in charge of the grownups. Littlefoot likes the idea and starts to hang with them more, snubbing his friends. Eventually, he'd go with them on the quest, though, heading down, he'd back off. However, the leader of the bad group, perhaps an evil Longneck, would have some members of the Gang of Five kidnapped to persuade Littlefoot to go. They would go near the fabled stone, which would be in a deep underground cavern in the Great Valley and would be sorta under the Smoking Mountains. A fight would occur underground and the stone would be lost. The bad guys are punished by the grownups, rather than killed or banished,, as they are just kids. Littlefoot would be punished too (for once!!!!) for his role, though to a lesser extent.
4.) My ultimate villain, an evil Gallimimus named Gallim who would speak both Sharptooth and Leaf Eater. He'd misdirect leaf eaters, easily posing as them as he can eat green food and speak their language. He'd then help his Sharptooth partners, who would be hiding on his orders, and then, he'd lead them to the leftover part of the herd that wasn't misdirected and they'd attack them and split the takings.
One of his first victims would be Mama Longneck, though Sharptooth would mess up things and go for Littlefoot and Cera, rather than Littlefoot, his mother, and his grandparents when they were asleep. The villain is easily able to change plans quickly. He ordered Sharptooth to kill Mama Longneck, which Sharptooth happily did. However, he assumed that Sharptooth and Cera had died in the Great Earthshake. Having thought Mama Longneck dead too, he tries to eat Littlefoot, but cannot catch him and vows to get him someday. He also gives himself the title "The Terror of the Mysterious Beyond". (the way I got him to work is to have him not seen so nobody would know his identity as a villain till it was revealed to one of the main characters and also had him off all camera shots of the original film but still be around then. He's basically like how they appeared to have the carjacker kill Uncle Ben in the Spider Man film but had it turn out to be Flint Marko in Spider Man 3., though, Sharptooth still would be Mama Longneck's direct killer, but Gallim would turn out to be the accomplice nobody knew about and indeed the mastermind of the operation.)
Gallim would return about 20 years later after that incident, though perhaps sooner if I could make him appear with voice only in some episodes I had planned for the TV Series, and would come to the Great Valley, having taken over most of the Mysterious Beyond (minus some place called the Valley of Sharpteeth, which he eventually takes over too via his servant Red Claw (yeah, Red Claw serves him. I had him give Red Claw his good looks and so even Red Claw fears him.) ) The villain would eventually cause a breakup in Littlefoot and Chomper's friendship and also cause the death of the Old One.
As he rises in power, he gets the Great Valley herds to fight each other, trying to recreate herd segregation within the Great Valley.
At some point near the end, he'd decide that Chomper is about to expose him and reveal his true nature to the Gang of Five. He'd then unleash a big army on the Great Valley.
Eventually, it would come down to a final showdown between him and Littlefoot and Ali in the Mountains that Burn, where he'd ultimately be knocked by a tail whip (shown to be one of the few things he is vulnerable to) from Littlefoot and fall into the lava and die. He'd be my finale villain. He'd have the most infamous villains of the franchise at his command (specifically, Sharptooth, Sierra, and Red Claw) at various points in the film.
(Note, he'd appear both in a flash back and even when Littlefoot is grown up, the final fight actually being on the very day and around the very hour Littlefoot comes of age in fact.)
