Wailer are ghoulified Crystal Ponies. They retain most of their emotional connection with one another that allowed them to power the aurora emitted from the Crystal Tower. However, due to the corruption, they mutated and irreversibly changed, turning them into yet another abomination of the wasteland. They retain many memories of their lives, and have exceptional communal abilities; that means they can share their emotions and memories, most of the time inadvertently or by force. It also means they share a hive-mind; if one Wailer experiences something they personally deem significant, all the others do as well. This includes the detection of trespassers, recalled events of the last day, or the death of another Wailer.
Wailers appear as bizarre, ghastly creatures. Due to the corruption of their bodies, their bones retain natural properties; their flesh and skin, however, retain that of the normal crystal pony. That is to say, their flesh and hide is transparent, allowing outsiders to view their organs and skeletal structure through otherwise transparent crystalline meat. Organs, veins, and bones are visible through a Wailer's otherwise clear muscle and skin. This can lead to a sickening skeletal appearance, which is wrapped in veins and holding thicker vital organs such as the heart, lungs, intestines, and stomach, all of which seem to appear as functional.
They are collected within the remainder of the Crystal Kingdom, known as Sorrow. They are considered abominations. They are shot on sight should they approach areas of dense Crystal Pony defense, due to their corrupted nature.
Through eye contact, they are able to project their memories and emotion contained within the memories they retain. Often times, this is of the final moments they experienced during the Last Day. They can recall not only the events of the terrible date, but the sensations and what they felt when the Megaspells fell, and the years afterwards in which they were irradiated and their perception destroyed. They can inject this into other ponies very quickly, crystal or not, via eye contact. For this reason, they are hated, ostracized, and immediately killed should they present any kind of perceived threat.
They have an unparalleled resistance to magical weapons, absorbing the attack, and are capable of a "midas touch" after a magical assault. They are infused by the energy of spells and magical weapons, which disperses through physical contact with another living being.
When they touch another being the spell will trigger and disperse from them as if they were a battery containing the spell. IE- If in the area of effect of a large healing spell, they will disperse this healing effect once touched by another living creature. The same can be said of malevolent spells such as disintegration; if they are shot with an M.E.W., they will absorb the spell, containing it (and often glowing as a visual side effect), and the next physical touch will disperse the spell into whatever being they are interacting with (disintegrating them, in the mentioned case).
Numerous shots can pierce this resistance, however. Once the attack spell "overcharges" the flesh and reaches bone or thick organs, it will act as normal, and disintegrate/melt/otherwise destroy the Wailer's vital body parts. This can lead to exceptionally gruesome, often disturbing deaths, as the destruction of the organs is visible through their crystal flesh and the wailer will still be alive for a short time after their skeleton has been burnt/melted/destroyed.
Otherwise, they are quite fragile. Their meat treats physical trauma like glass treats a baseball bat. If they are struck with a rock, for example, their flesh will crack and break. This makes them exceptionally brittle to any normal means of attack, like bullets or bludgeoning. Approaching them, however, is not recommended, as it only takes one good look in order to completely control or destroy a brave adventurer, and they tend to condense around areas of strife- their numbers are expected to be in the thousands, as they are the population of the entirety of the Crystal Empire, and have not wandered.
They are always seen, or heard, crying. Due to the memories that infest victims of their psionic abilities, it is surmised that they are in constant, cyclical mourning and remembrance of the Crystal Empire and how it was destroyed on the Last Day. It is also assumed they only wish to escape this repetition, by evacuating their memories onto other unfortunate souls.
They are only seen within the Far North, near the remains of the Crystal Empire. They are confined to unspoken habit; they remain near their old homes within the Crystal Kingdom. They reenact events from before the war, traveling to the remains of grocery stores, libraries, and public events that never actually happened due to the holocaust. It is believed they are unaware that they outlasted the balefire attack, and are in a collective illusion to disregard the event. They are often heard weeping, calling out names (which are assumed to be friends, lovers, or children), and screaming "Take cover, the bombs are coming." These events repeat once each day within Sorrow, their named location.
Though they are frail, they are not to be underestimated. They have an innate psychic link with other crystal ponies, and eye contact transfers not only memories, but the emotions of those moments to a victim. Many of the afflicted commit suicide; often times, Crystal Ponies turn into Wailers themselves, simply through meeting eyes.
For more regular ponies, Pegasi, Earth, and Unicorn, they are not so dangerous. Wailers still retain some level of lethality, however, as their memories can overwhelm and demolish a mind. In the worst cases, victims have their minds "overwritten," resulting in them truly believing they are a completely different pony (the wailer that assaulted them). In others, it inspires schizophrenia or a split personality, as the memories and feelings of the Wailer combine with the victim's natural thoughts indiscriminately.
Even if these events do not occur, Wailers are not kind. While the victim is entrapped within the memory one Wailer projects, the other Wailers will close in on a memory-afflicted victim to eliminate the threat and maintain the collective illusion. They will beat, bite, and otherwise kill the unaware and sensory deprived victim en-masse in order to return to their memories. Wailers that were police or military officers are especially dangerous, as they appear to retain all knowledge and skill from being trained with weapons they posses, and can recall it when threatened. This results in single-minded ghouls that, when disturbed, are actually excellent marksman while willing (and able) to utilize exceptional pre-war and team tactics before returning to aimless wandering.
This mental ability is able to extend indefinitely in terms of distance. It has been noted to harm others through binoculars, rifle scopes, and even visual recordings. In some cases, the audio recordings of their weeping has been known to disturb listeners to such extremes that they will refuse to even acknowledge the existence of Wailers, calling them "f*cking superstitions" and "nothing but damned ghosts."