To be a Wraith is to be a spiritual echo of what once was. And though it's true an echo will last longer than the sound that originally made it, it tends to get weaker and more diluted as time goes by. As above, so below.
 
To the dead there is no question of the heart and mind ruling the body or not - they ARE the body, and the body is them. Wraiths are thought and feeling wrapped inside ghostflesh, ever in danger of being undone from without or within. And while Wraiths might be a little hardier than most, even they have their limits.
 

Body is Soul
 
A Wraith's appearance is largely dependent on how "together" she is: a combination of how she's feeling, how much Essence she has in her, and the overall strength of her Corpus. Given all that, a Wraith might change her looks fairly often in the same day, even without consciously Shaping herself.
 
A Wraith tends to wear her emotions on her sleeve, unless she's very good at hiding them. Those who are upbeat and happy appear brighter, as though they were out in the sunlight, while a Wraith who is dejected or upset seems dark, as if caught in the shadows. Those who are sad seem wet and clammy, as though they'd soaked themselves with their tears, and those who are angry seem hot to the touch, and may even steam with rage. And so on
 
Wraiths with a lot of Essence seem to move faster, and glow with an inner light that illuminates their features and stands out against their Deathmarks. They also have more color to them than your average Wraith, which is still considerably muted when compared to the world of the Living, but is a welcome change from the normal dull palette of the Deadworld. Those with very little Essence to them are duller than usual - almost colorless, in fact - and seem to move slower, even if there is no real reduction to their speed.   
 
Corpus, meanwhile, is measured in two ways by Wraiths: how much they have at the time, and how much capacity they have for it. Those with a fairly normal capacity are solid in appearance, while those who aren't are translucent, transparent or practically invisible, depending on how little room they have for Corpus. And while those with a fairly full "tank" have distinct features, those who have lost most of their Corpus are fuzzy, indistinct or unclear, as though they were losing cohesion due to damage. This lack of clarity is on top of whatever other damage might have been done to the Wraith, such as losing a limb, having been raked across the face by claws or burned severely.
 

Soul Damage
 
A Wraith's Corpus is a bloodless sack of soulstuff - one intangible to most of the slings and arrows from the Land of the Living. However, when faced with dangers from her new world, a Wraith's body proves as malleable and fragile as the flesh she left behind at death. Wraiths can be punched, kicked, cut, mashed, sliced open, dismembered and burned, just as any mortal. And while they are in no danger of having bones broken, bleeding to death, or suffering the loss of a vital organ, the pain caused by their equivalent remains as acute as ever.
 
That said, it is difficult to destroy a Wraith through the application of brute force alone. Only the most serious kinds of damage, done in an overwhelming amount, can utterly destroy a Wraith on the spot. All other kinds of damage done to them might indeed shred their bodies to nothing, but they will reform near their closest - or most powerful - Anchor within the hour, provided they can overcome their Shadows' attempts to keep them from reforming.

Ossification

A Wraith's essential oneness of body and soul can produce physical effects that are not merely cosmetic. Perhaps the most pitiful is being spiritually "frozen" by an extreme lack of inner drive. This state is known as Ossification, and it can strike anyone, at any time.
 
Over the years, a Wraith may tire of the endless, seemingly-pointless expanse of time that is life after death. If she doesn't recognize that this is a problem, and gives in to ennui, boredom and depression, she may find herself slipping away. Hours will slide by as swiftly as minutes, days will pass with little note, and she will question the need to do anything ever again. After all, what would be the point?
 
Wraiths who succumb to this line of thinking find that their bodies are a willing accomplice to the crime of soul-surrender. They begin to reject Essence, which makes them feel dull, gray and unmotivated. Then their Corpus gradually turns as white as marble, and becomes just as unyielding and immobile. Cobwebs form in the air around them, binding them tightly to wherever they chose to make their final resting place.
 
And if they do not snap out of their funk, and no one intervenes, such Wraiths one day close their eyes one last time, and fall back Asleep.
 
It's important to note that a Shadow cannot cause a Wraith to Ossify. It can, however, steer a Wraith towards that state of mind by judicious use of its Thorns. {It can also pull the Wraith back from the brink, and set her back into motion, but why would a Shadow want to do that?}

Getting Lost

Another danger of the mind and body being one in the same is what the Shadow can do to a Wraith's senses, body or immediate circumstances. If left unchecked, it can completely rewire how its Wraith receives information, putting her into a sinister, virtual reality known as being Lost. And a Lost Wraith is a serious hazard, both to herself and to others.
 
The living speak of delusions: seeing and hearing things that aren't really there, or failing to see things that are. But while those illusions might be tricks of an unbalanced mind, to the dead they may be everyday occurrences, spawned by their Shadows. These tricks are known as Thorns, and much like their namesake they are painful and entrapping.
 
Most of the illusions a Shadow can make with its Thorns are of short duration, only. However, it is possible for a Shadow to make such a trick last for much longer, and then keep it going, so as to really fool its Wraith. And as a Shadow gains in power, it can keep more and more Thorns going at once, eventually getting the Wraith to a state where almost all she perceives, says and does is a product of her Shadow's will.
 
Wraiths who have reached this sorry state of affairs are referred to as Lost. They are rarely pleasant to be around, as they may look grotesque and invite trouble on themselves. They might interpret all friendliness as hostility, and all offers of help as sordid, demeaning suggestions. They may even start to see friends as foes - and foes as friends - and lash out against anyone who tries to bring them out of it.
 
It is for this reason that the Pardoners are so extreme in their methods. They won't tolerate any dissembling, as they know it could be the Shadow covering up a cry for help, and treat all their flock as though they were in need of desperate scourging. They figure it's better to have been a little overzealous in a situation that didn't call for it than to be criminally kind to someone needing tough love.
 

Damnation

All Wraiths have a preternatural fear of The Damned - not only because they are so hostile towards Wraiths {ravenous might be a better word} but because they know that behind every fanged maw and taloned hand is a face that was once just like their own. Each and every one of their deadliest enemies were Wraiths, and they are an ever present reminder of what happens when the Shadow wins.
 
One might wonder, then, why so many Wraiths succumb to Damnation? It should behoove anyone with a sense of self-preservation to look well upon the Damned, and consider their own position.

The answer is a sad one: the more power a Shadow has, the more its Wraith becomes like it.
 
As the Shadow grows stronger, it is able to subtly influence the Wraith's thinking. It starts out with small, little decisions, such as whether to lie, but eventually goes up to much larger and darker sins. And as these dark acts weigh upon the Wraith, the Shadow gets stronger still.

Before long, the Wraith reaches the point where she sees less and less reason to care about keeping her dark side in check. Aren't their goals essentially the same, now? Aren't they stuck with one another, thick and thin? "Detente" becomes the watchword, rather than "victory," and cooperation with the darkness becomes a daily convenience rather than a frantic act of dire emergency.

By this time, both halves of the personality are on near-equal footing, and there is precious little difference between the Wraith's point of view and the Shadow's. One day she will ask if it really be that terrible to be united with their inner darkness, once again. And after that it's a slow but sure spiral into Damnation - one that only the greatest expenditure of self-will, or the most powerful acts of a Pardoner or Ferryman ,will halt.

And even they cannot reverse the damage that's been done. "Once fallen, always scarred."