After two minutes and thirty seconds has passed since spawning, it re-grows a head and gains 25% HP.
After another two minutes and thirty seconds has passed again, it will cause Tinnin to regrow its final head and regain another 25% HP and the auto-regen will vanish.
Impossible to defeat until both heads have respawned.
Every time Pyric Bulwark (physical shield) or Polar Bulwark (magic shield) is used, Nerve Gas will be used immediately after.