The Longneck From the Past is a 20th episode of the animated television series, Land Before Time All Grown Up involving Littlefoot who encounters Longpata, his grandfather's arc enemy that wants him to join him or perish.
In the Great Valley, Littlefoot and Chomper were being chase by Cera who after pranking her and a herd of leaf eaters (Maiasauruas) were running cause a pack of Rogue Runners (Gallaminus) are in the Great Valley and they start attacking them and during the fight, the Rogues are after Littlefoot, and Chomper and Cera backs him up.
After the fight, their leader Gallaminer told Littlefoot that he will join the Longneck who lives in the Mysterious Beyond soon.
When Littlefoot heard what Gallminer said about the Longneck in the Mysterious Beyond, he went after the Runners to find out why he there.
Littlefoot (Eljiah Wood)
Cera (Hayden Panettiere)
Ducky (Tara Strong)
Petrie (Tom Kenny)
Spike (Mitchell Whitefield)
Tippy (Rickey D'Shon Collins)
Chomper (James Arnold Taylor)
Ruby (Grey Delisle)
Longpata (Clancy Brown)
Skip: Hey, speaking of Littlefoot, where is he anyway?
Cera: Littlefoot? Oh, yeah, right. Littlefoot's gone into the Mysterious Beyond after those Rogue Runners that were after him, but he'll be back soon.
Chomper:Yeah, you know Littlefoot. He always comes back.
Tippy: Why were those Rogue Runners in the Great Valley?
Ruby: And why were they after Littlefoot?
Ducky: And why did Littlefoot go after them in the Mysterious Beyond?
Chomper: He wanted to know why there's a grown up longneck living there.
Petrie: A grown up longneck in the Mysterious Beyond?
Chomper: Yeah, I know. Weird, right? Who ever heard of a grown up longneck living in the Mysterious Beyond, huh?
(The dinosaurs gasp after what Chomper said)
Mr. Thicknose: No! No, no! Not him! Not Longpata!
Cera: Who's Longpata?
Mr. Thicknose: Longpata is a very dangerous longneck who lives in the Mysterious Beyond. Littlefoot's grandfather, Grandpa Longneck got him exile before any of you were born.
Ruby: Why did Littlefoot's grandfather get a longneck exile?
Mr. Thicknose: Because Longpata did very bad things over the past years.
(Showing a Flashback of the day Longpata was banished to the Mysterious Beyond)
Mr. Thicknose: Grandpa Longneck told me after Bron went to find a home for him, his wife, and his grandson Littlefoot, Longpata attacked many Longnecks.
(Longpata roaring while killing the longnecks when Grandpa Longneck came)
Grandpa Longneck: Longpata! Get away from them!
Longpata: Whatever you say, old one. I was looking forward to kill you.
(Grandpa Longneck and Longpata fighting)