Stealth monster
Stealth monsters are monsters which are normally invisible. They become briefly visible when they receive damage, fade out of visibility when calling A_Look, A_LookEx, A_Chase, A_ExtChase, A_FastChase, A_VileChase. They fade in, on the other hand, when calling A_FaceTarget, A_FaceTracer, A_FaceMaster, A_MonsterRail, A_CustomRailgun, or A_CPosAttack. (Note that practically all attack functions call A_FaceTarget.) Finally, the monsters become and remain visible when calling A_Fall, A_NoBlocking, or A_FreezeDeath.
Creating a stealth monster in ZDoom is easy: merely adding the STEALTH flag and giving it an Alpha of 0 is enough. Note, however, that when a stealth monster is visible, its render style will always be "normal". A fuzzy, shaded, additive, translucent, etc. stealth monster will not work; the stealth implementation directly changing the actor's render style.
By default, ZDoom provides stealth variants of the Doom II monsters except the spectre, the cyberdemon, the spiderdemon, the pain elemental and the Easter eggs Commander Keen and Wolfenstein SS:
- StealthArachnotron
- StealthArchvile
- StealthBaron
- StealthCacodemon
- StealthChaingunGuy
- StealthDemon
- StealthHellKnight
- StealthDoomImp
- StealthFatso
- StealthRevenant
- StealthShotgunGuy
- StealthZombieMan
A stealth spectre would be indistinguishable from a stealth demon, stealth bosses would be quite unfair, and the Easter eggs' presence in mod is generally frowned upon as an amateurish mistake.