You searched for INVISIBILITY MASS INVIS
1. invisibility mass invis
Syntax: cast 'invisibility' <character or object>
The INVIS spell makes the target character invisible. Invisible characters
will become visible when they attack. It may also be cast on an object
to render the object invisible. INVIS also protects vampires from the sun.
including the caster.
Those affected by true sight can detect invisible players.