The Buddy System badge is awarded when you and a player from your Roblox friends list join a game of Doors together. ... Seek appears twice: once between doors 30-45 and again between doors 80-95.

Seek has two options for you to choose from. You could either play the role of a Hider and hide in the title's massive world, or be a Seeker and tag every Hider in the game.