Ghosts’ appearance depends on several factors, but the largest one is based on that of the Unicorn’s magical prowess when alive. Exceptionally powerful unicorns take on a spectral form that is mostly the same as their mortal form, while average and weaker unicorns lose clarity and shape depending on how skilled they were at magic. Magic is what keeps ghosts from fading away into the wind, and they can temporarily become tangible so they can interact with objects and mortal beings. Weaker unicorns can struggle to stay tangible for longer, if even at all.
Ghosts are typically monochromatic in color, with the distinct exception of their eyes retaining their original color, while still becoming monochromatic. This color is usually based on their coats, but can come from their cutie mark or hair.
When tangible, ghosts can look indistinguishable from normal ponies, but as their magic weakens, their colors fade until they are no longer visible as normal. Ghosts can go in between being invisible and visible at will, again based on magical prowess. Visibility and tangibility are not linked, so it’s possible for a ghost to make themselves tangible while still being invisible, this means a lot of ghosts are tricksters and use their powers to screw with ponies or cause general mischief.
Ghosts are essentially condensed magic in the shape of a pony, ghosts sometimes emit a magical essence from their ‘bodies’ that looks like colored smoke. This magic essence is too weak to do anything or be useful, however, it’s also always visible, so it may give away an invisible ghost’s presence. When tangible, ghosts feel very cold and may even be slippery and wet, thanks to a thin layer of ectoplasm. Ghosts don’t hold themselves very well in heavy winds or storms. Wind can disperse their ‘bodies’ to the point of being entirely scattered permanently if their magic cannot hold them together.
Ghosts don’t need to eat or drink at all, and doing so can only slow them down. They can still do it, but it will go right through them, literally. Ghosts are often magically tethered or bound to locations, objects, or mortals as a part of their curse. This limits their haunting grounds to the area, or wherever the object or mortal are. If ghosts are bound to mortals, they either make the mortal’s life a living hell or form a bond with them.
Ghosts can perform sexual acts when tangible with mortals, but can always have sex with other ghosts regardless of tangibility. Ghosts more often use this power to fuck with mortals, literally, but they can be intimate too, they just prefer to be playful tricksters instead. Ghosts jizz ectoplasm, which feels similar to normal jizz, but it fades away over time and is uniquely colored per ghost.
If a ghost was a a non-pony in life their spectral form will represent that, but nothing else will change skill-wise.