Usage: invis [level]

INVIS sets your invisibility level.  With no argument, invis toggles between
making you fully visible and fully invisible.  If you specify a level, only
people at and above the level you specify will be able to see you.

Examples:

  > invis
  > invis 31

Exception: Levels 1 - 9 are immortal invis levels. Going invis at these
            levels will only allow immortals <level>+ to see you.