Ring of Perception

Ring of Detect Invis, basically. Here, too, is an "adding solution" for
the problem of Purge + Invis Ring, which is an overpowered and
unanswerable strategy.

This ring shares art and sound with the invisibility ring, as well as
duration, but it drops off of narthyl worms.

It has the appropriate checks to avoid overlap with the Detect Invis spell itself,
and I saw no errors in the log or problems in testing. Putting on the ring
reloads objects in the room, immediately showing invisible battlers. Taking the ring
off does the same in reverse.