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About Terriermon;
Terriermon started out as a wild Digimon, fighting by the rules of the "survival of the fittest" doctrine in the harsh realm of the Digital World.[1] When Henry received a Digimon video game as a present from his father, he selected Terriermon to play with because he identified with him (he said he wanted to be challenged by a small digimon). During a battle between Terriermon and Gorillamon, Henry caused Terriermon to Digivolve into Gargomon. However, Gargomon lost control of his powers and Terriermon was nearly unconscious when he De-Digivolved, causing Henry to regret causing Terriermon's digivolution. Soon after, the mysterious Blue Card was discovered among Henry's card collection. Henry swiped the card through his card reader, transforming it into a D-Power. Terriermon then Bio-Emerged into the Real World as Henry's partner.
At first, Henry hid Terriermon from his family by making Terriermon act like a simple stuffed animal. Later, Terriermon met the other Tamers, and became fast friends with Guilmon (Takato's partner).
Terriermon has a laid back personality - and often uses the word "Momentai", a Cantonese phrase that means "take it easy " or more commonly, "not a problem".
Appearance;In the English dub, Terriermon was called a bunny because of his long ears and his similarity to Lopmon. However, he is actually modelled after a dog, and named after a group of dog breeds Terrier.
Terriermon digivolves into the following:

Rapidmon

MegaGargomon
And also de-digivolves into Gummymon, which is Terriermon's in-training form.
Credits: this page and Wikipedia

