Gun Vendor Easter Egg in Halo 5: Guardians
The Gun Vendor Easter Egg in Halo 5: Guardians can be found in mission 3.
Exit the big gate at the beginning, to enter the first battle in the mission. Go to the buildings on the right side and enter the small room on the bottom floor.
The Gun Vending Machine is in here. Keep pushing the button to get different weapons out of it. You will also hear the “Grunt Birthday Party” sound effect.