Did you know? There was a Terriermon BEFORE the one in Tamers! He appeared in the double movies that belong to the Digimon Adventure 02 series, titled "Digimon Hurricane Touchdown" and "Supreme Evolution! The Golden Digimentals." I call this Terriermon "Prototype Terriermon," and although he appears in his Baby, Child, Adult AND Armor forms, he's called Gummymon throughout the entire movie. This is probably because his partner Wallace is too busy getting girlfriends and becoming fluent in foreign languages to care about technical Digimon stuff.
Personality-wise, Prototype Terriermon is a fierce little guy who won't hesitate to fight for even a second. He has a lot of disagreements with his partner, but would do anything for him if he'd need to. He also seems a lot less serious than Wallace since he fooled around with Daisuke and V-mon a lot.
So here's the story! The 02 kids are on vacation in America visiting Mimi when all the Adventure kids mysteriously vanish. Takeru and Hikari locate Wallace and Gummymon (actually Terriermon) right after a battle with a large monstrous Digimon, but upon noticing them, Wallace grabs Gummymon and runs off.
Wallace and Gummymon hop on board a truck and have a talk. "Wallace, I'm tired!" Gummymon says. "Wallace, are you going to the flower field?" No response. "Hey, Wallace! What's wrong?"
"What's wrong with YOU?" Wallace replies. "That could have been Chocomon! Attacking him of all things..."
"But he was seriously intending to attack you, Wallace!" Gummymon defends himself. "I just wanted to protect you."
"He might have understood if we tried to talk to him," Wallace says. "Attacking him of all things..." he repeats.
"But that guy... he's thinking about horrible things."
"I don't want to hear it."
"Got it. I won't say more." Terriermon walks over to Wallace and sits down next to him.
The two of them eventually get off the truck in order to phone Wallace's mom. They hitchhike into another, only to meet up with Daisuke, Miyako, Iori and their Digimon who are on their way to find Takeru and Hikari! Chibimon recognizes Gummymon as a Digimon, and all of them get off the truck and have a talk about Digimon and stuff. Wallace surprises them with his ability to speak Japanese, and he tells them it's because he had a Japanese girlfriend once. Some kid! We are all inferior to Wallace.
Miyako and Iori get on another truck, but Wallace, Daisuke and their Digimon stay behind. Wallace tries calling his mom again, who is very worried about him. That's when Chocomon appears! Chibimon evolves and starts attacking him, Gummymon following his example and evolving into Galgomon. Wallace stops the fighting, but Chocomon disappears. "I'm waiting for you at the flower field!" Wallace calls out to him.
Riding Lighdramon, Wallace and company eventually catch up with Miyako and Iori. Gummymon says that he believes Chocomon wants to be reunited with Wallace and for things to be like they were back when they were small, which is why he's gathering kids with Digivices like Wallace's and shrinking them. They continue their journey, but have to camp outside for the night. Wallace and Daisuke have a talk, and it's revealed that Chocomon is Wallace's other Digimon who hatched from the same egg as Gummymon, and that he disappeared seven years ago when the three partners were playing together in a flower field. That's why he's on his way to said field - he hopes Chocomon will be there and turn into his old self without having to fight.
They reach the flower field the following day, and do indeed meet up with Chocomon there, but he's too pained to listen to reason. The Digimon all have to fight him, and he evolves into Antiramon and then Cherubimon. Takeru, Hikari and their Digimon show up, and the latter evolve into their Ultimate forms, Seraphimon and Holydramon, in order to give Wallace and Daisuke a golden Digimental each. Using the Digimentals, Gummymon and V-mon evolve into Rapidmon and Magnamon respectively, and manage to destroy Cherubimon.
"Chocomon..." says Gummymon. "He smiled."
Time for some goodbyes! Daisuke says he's sure Chocomon will return, and Wallace says he wants to come visit them all in Japan one day. The story ends with Wallace and Gummymon finding a Digimon egg, and after the credits, Wallace can be seen together with both Gummymon and Chocomon, as Terriermon and Lopmon.