Devoted players have spent years creating speedruns for "Doom", competing for the quickest completion times and sharing knowledge about routes through the levels and how to exploit bugs in the "Doom" engine for shortcuts. Achievements include the completion of both "Doom" and "Doom II" on the "Ultra-Violence" difficulty setting in less than 30 minutes each. In addition, a few players have also managed to complete "Doom II" in a single run on the difficulty setting "Nightmare!", on which monsters are more aggressive, launch faster projectiles (or, in the case of the Pinky Demon, simply move faster), and respawn roughly 30 seconds after they have been killed (level designer John Romero characterized the idea of such a run as "having to be impossible"). Movies of most of these runs are available from the COMPET-N website.