Assuming this hasn't already been added without me noticing.. A way to selectively hide objects from players would be very nice, if not vital for certain things. Example:
/mob/ghost
seen_by=GHOSTS
view_group=GHOSTS
This could be done using bitfields, or maybe(though slower) lists. When atom.invisibility isn't enough anymore, something like this would be really necessary.
Such as you can make ur own bitfield stuff to use such as GHOSTS as what you have and PLAYERS, maybe LIONS too.
I would use this so only GHOSTS can see GHOSTS and NormalPlayer can't. And such.
I even tried working around stuff like this using image() but it failed because apparentally image() will follow a users direction but it fails to do the walking animation, it does animation in general though but doesn't respond to you moving. Which in itself should be fixed if it allows the icon to change at all, for animation or even otherwise direction then it should technically work for moving animation too.