Froggy

"Froggy... Where are you?"

Froggy (カエルくん) is a large green frog with yellow eyes with black pupils, and the pet and best friend of Big the Cat.

History
During the course of Sonic Adventure and part of Sonic X, Froggy swallows both a part of Chaos and a Chaos Emerald. Abducted by E-102 Gamma, Froggy was taken to the Egg Carrier as Doctor Eggman wanted the Emerald and Chaos piece inside him. Big pursued him, and recovered his friend. However, the Chaos Emerald and the part of Chaos he had swallowed were absorbed into Chaos, allowing it to become Chaos 6, but was eventually rescued by Big with the aid of Sonic. Big and Froggy then took the Tornado 2 back to Mystic Ruins.

In Sonic Heroes, Froggy and Chocola, a Chao, were abducted. Big, Amy and Cream went to look for them under the impression that Sonic had taken them. During the adventure they instead figured out that Eggman had kidnapped Froggy and Chocola, and defeated him. However, it turned out that Metal Sonic had framed Eggman, and had kidnapped Froggy and the Chao in order to copy the residual data of Chaos. Froggy was not seen in the final scenes of the game, but it can be assumed that he and Big went back to Mystic Ruins.

He appears in Sonic Chronicles: The Dark Brotherhood in some of Big's POW moves. In an optional mission, it is known that Froggy has a friend who is also a frog named Norton who Froggy hadn't seen in a while and was concerned about. In the process of trying to find Norton, his other friends, Gally, Mr. Billywick and Mrs. Stevens are found (and appear to have very active social lives, according to Big's dialogue).

In Sonic Adventure, Froggy weighed 500g (3lb).

In Sonic & Sega All-Stars Racing, Froggy returns as Big's All-Star Move. After Froggy hoped on Big's head, he suddenly turned into Giant Froggy. Big's all-star theme is and...Fish Hits! from Sonic Adventure.

Theory
An interesting suggestion is that Froggy originates from "Frog Forest", a level in Sonic Heroes, which has giant frogs that can summon forth rain and bear a very strong resemblance to Froggy. If the player stands around in Frog Forest for some time as Team Rose, Big himself also presents this theory.