A_ClearShadow

This spectre becomes visible if its health goes below 30 (provided it enters its Pain state at least once):

Actor Spectre4ZDoomWiki: Spectre replaces Spectre
{
  States
  {
  Pain:
    SARG H 2 Fast
    SARG H 2 Fast A_Pain
    SARG H 0 A_JumpIfHealthLower(30, "MakingVisible")
    Goto See
  MakingVisible:
    SARG H 0 A_ClearShadow
    Goto See
  }
}