UPDATED LIST OF THINGS THAT ARE INVISIBLE -
White Dragon 3 skull boss from the… Cimmerian(?) or Nordheimer Purge
the golden lotus near the volcano obilisk is invisible
invisible elephant calfs, tigers, panthers,
greater yakkiths, Black Yeti, King Rhino, Rockslide, Avalanche, snake men brutes, camels, yetis, elephants, the lion king on swagger rock, the Abysmal Remnant is invisible and all you see are its eyes now and after killing it the crafting book it guards is missing both online/offline.