There are three GOOD Chomper possibilities (Codename Luke Skywalker (note, don't know where films VII - IX are going, but, assuming from what we've seen so far.)
1.) He DOES eat Leaf Eaters, but outside the Great Valley, and Littlefoot and the Gang of Five and Ruby and Chomper engage in Don't Ask, Don't Tell policy about what he's eating.
2.) He eats Tickle Fuzzies (mammals. There might be some big ones that will fill him.) and also eats Egg Stealers. (Egg Stealers can't be loved in the Great Valley.) Also, maybe he eats Fast Biters.
3.) Also, he can eat fish and any bad Leaf Eaters out there. Perhaps he can eat bad Dome heads.
(4.) He could eat Yellow Bellies and Rhett. Just kidding!
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There are also some, really frightening, BAD Chomper possibilities (Codename Anakin Skywalker, the hero who went bad)
1.) He does get older. Eventually, out of fear, they cast him out. He becomes sour, eventually blaming the Gang of Five for not sticking up for him. As he knows a lot about the Great Valley, including likely its many entrances, where Tree Sweets would be and hence where not to go, and also what points one could sneak around and not get caught, and, for revenge on everyone, blabs to loads of Sharpteeth and they attack in the middle of the night. Eventually, he and Littlefoot would fight and Chomper would die as the final villain of the series.
2.) He is broken by Red Claw and tells Red Claw how to get in and bla bla bla. Eventually, after Red Claw does some harm, he feels tainted and joins Red Claw, feeling that he can't be friends with the Gang of Five anymore.
3.) It is revealed that, for some sinister reason, pretty much his whole friendship with the Gang of Five and Ruby was a ruse to harm the Great Valley and others.
4.) He indeed cannot find enough to eat and tries to eat Littlefoot, perhaps resulting in his death, and maybe Littlefoot, who seems too trusting of him, getting scarred on his body from the encounter.
5.) He just leaves the Great Valley and hunts leaf eaters out there, realizing that they won't like him in the Great Valley forever. In this case, he's only dangerous if he encounters them outside the Great Valley, and if he is feeling mad at them.
6.) He gets stronger as he gets older and becomes power hungry, deciding to use his strength and above average intelligence and ability to speak Leaf Eater to try and take over dinosaur places in hopes of ruling the dino world with an iron fist, thinking himself to be its rightful ruler because of the gifts he has.
7.) He would have stayed good, but, after finding a love interest, one who doesn't care for leaf eaters except as food, ends up hunting leaf eaters, if more for her than for himself.
8.) It turns out that Sharptooth from the first film is a relative of Chomper's. After Chomper finds out the Gang of Five killed Sharptooth, he begins plotting their ends in order to get revenge for Sharptooth's death.
9.) He hides in hidden parts of the Great Valley, and uses his knowledge of how leaf eaters operate and stuff, to know their strengths and weaknesses so he can know what to do when encountering them, and, as such, becomes so dangerous that that part of the Great Valley is considered perilous.
Of course, there is also the heroic sacrifice options too.
1.) Red Claw is gonna kill the others, so Chomper gives up his life to save the Gang of Five and Ruby.
2.) An older Chomper leaps in the way of Red Claw or some other Sharptooth and is impaled, but this gives Littlefoot the chance to live and beat Red Claw or whoever the attacker was and avenge Chomper.
3.) Chomper does go after them, feeling hungry, but, knowing they are friends, ends up letting himself die in an Earthshake or fall into a volcano so that his friends can live.
Also, there is this possibility, though it would be a huge sacrifice on the part of the Gang of Five and Ruby.
1.) Chomper is kicked out, or, fearing he'll harm the Great Valley, leaves on his own. The Gang of Five and Ruby leave the Great Valley, never to return (or rarely to return) so that they can be with their friend, willing to risk even their own deaths.
However, the scenario which seems the best movie wise would be, that things get set in motion as he and the Gang of Five near adulthood and his loyalty is unknown, seeming to shake back and forth, but, at the climatic moment, he joins the heroes and defeats the bad guys and is allowed to stay in the Great Valley for life. This one would be the best of both worlds, seeing a tension between him and the Gang of Five that we've never seen before while at the same time avoiding permanent enmity or even Chomper's death. Or, if he doesn't want to live in the Great Valley, can live somewhere he can live nearby, perhaps with other Sharpteeth, including a family of his own, and he will eat Egg Stealers or whatnot and not Leaf Eaters and try and teach Sharpteeth to be nicer, and also he'd visit the Great Valley often.
Anyway, cross dietary friendships are quite prevalent in other films, including another one done by Don Bluth.
1.) Fieval and Tiger
2.) Simba and Timon and Pumba
3.) Luis and Naveen and Tiana
4.) Diego and Manny
5.) Alex and Marty
True, we could see something similar to what happened with Alex and Marty, but, hopefully, that's as far as it will go.
