If the HoIO is a walking bestow curse, then the phantom is a
walkingfloating fear gaze. This CR 3 hazard is more annoying than anything, as it can induce fear but cannot truly attack or harm the living. The best way to deal with it is to dismiss or banish the spirit away.
Believe it or not, piercers deal piercing damage; 1d6 for a small one, 2d6 for a medium one, and 3d6 for a whopper. They are vaguely snail-like organisms with stalactite camouflage that allows them to hide unnoticed on cavern ceilings. If a creature walks under, the piercer releases suction, plummets downward, and impales the poor creature if it can't move away quickly enough.
A moss that puts you to sleep then suffocates you. Eh.