Developer is an achievement/trophy in the Metro: Last LightDLC, Developer Pack, awarded for spending at least 3 hours on the DEVELOPER level. This includes the Metro Museum, the AI Arena and the Shooting Gallery. It is unknown exactly how this is calculated, and whether 'cheats' such as setting your console clock forward three hours gets you the achievement/trophy. This can be done over multiple playthroughs, however, though it is also not clear whether restarting the level resets the timer. If you are struggling, leave the game running for three hours while you do something else, to get this.