Classes:InvulnerabilitySphere

From ZDoom Wiki

Invulnerability sphere
Actor type	Powerup	Game
DoomEd Number	2022	Class Name	InvulnerabilitySphere
Spawn ID	133	Identifier	T_INVULNERABILITY

Classes: Inventory→PowerupGiver→InvulnerabilitySphere

The invulnerability sphere is a green sphere with a grinning, red-eyed face appearing on it. When picked up, the player becomes invulnerable and see everything through an inverted white map.

If the item is imported in Heretic or Hexen, its effect when picked up will vary because it depends on the game and on the player class's Player.InvulnerabilityMode feature rather than by the item itself. See here for the details. If the item is imported in Strife, it'll behave exactly as in Doom.

DECORATE definition

ACTOR InvulnerabilitySphere : PowerupGiver 2022
{
  Game Doom
  SpawnID 133
  +COUNTITEM
  +INVENTORY.AUTOACTIVATE
  +INVENTORY.ALWAYSPICKUP
  +INVENTORY.BIGPOWERUP
  Inventory.MaxAmount 0
  Powerup.Type "Invulnerable"
  Powerup.Color InverseMap
  Inventory.PickupMessage "$GOTINVUL" // "Invulnerability!"
  States
  {
  Spawn:
    PINV ABCD 6 Bright
    Loop
  }
}

note: Invulnerability sphere respawns only if sv_respawnsuper is set.