The Valorant GO! Vol. 1 Killjoy Gunbuddy is sold when available in the store as a individual item for 475 valorant points or as a part of the Go Volume 1 bundle for 8700 valorant points.
Gunbuddies are charms that you can attach to any of your guns in Valorant. They usually come in pair of 2 so you can have them active in two different weapons at the same time. It’s also possible detach them and move to different guns.