At the end of Doom II players face off against The Icon of Sin, which is really just a large and creepy texture that spits out demons. But this boss fight has some odd mechanics and quirks, including a small programming oversight that could lead to players having to wait over a decade for a demon to spawn.
Source: Kotaku – It Can Take Nearly 12 Years To Spawn A Demon In Doom II Thanks To A Small Programming Quirk