The Goose is Loose
From Halopedia, the Halo wiki
The Goose is Loose is an achievement in Halo: The Master Chief Collection. It is unlocked by getting 25 enemy kills with the Gungoose on Halo 2: Anniversary multiplayer. The achievement is worth 10 Gamerscore and can be unlocked in both matchmaking and custom games. It also unlocks the "Gun Goose" Multiplayer Emblem.