Mongoose is a green creature type used for cards that depict slender, ferretlike carnivores that feed on rodents, birds, and eggs. Mongooses are especially noted for their ability to kill cobras and other venomous snakes, but this hasn't translated in the cards yet. They usually have shroud, and in one instance protection from blue.
The first creature to bear the type was Blurred Mongoose from Invasion, though Karoo Meerkat from Mirage was issued errata to become a subtype Mongoose as well (instead of Meerkat). The third and last printed card was Nimble Mongoose from Odyssey.