That animation was complete tonal whiplash from Ardenweald. It was hilarious in its way, but quite the 180 from how the other zones were portrayed in Afterlives.
Hiding the response behind headings in case you aren’t interested in spoilers.
Venthyr Culture - Heavy Spoilers
The culture behind the Venthyr is based along Western vampiric folklore, with several nods towards modern fiction in the ways they organize.
Denathrius is the ‘sire’ of the race as its progenitor, all of the Venthyr of the zone were once mortal beings that underwent the same punishment, sometimes over centuries or “millennia” to purge themselves of sin in a way that is not altogether different from the way the Kyrian do it. One obtains penance through pain, the other through distance. While the Kyrians simply destroy the expelled emotions, letting the anima seep into the ground and then extracting it later using pylons, the Venthyr seem to harvest these red Sha-like emotional manifestations of anima.
Each soul, when it begins its penance, has a sinstone that is engraved with a number of their sins. One of the newer ways of torturing souls, we discover, is affixing the stones to the soul as a physical weight that must be carried (ala Jacob Marley), we see that this is considered particularly cruel as souls will become maddened from the burden of the weight or be crushed into nothingness by it.
Anyways, back on point, it used to be a choice whether the soul went on to another afterlife or become a Venthyr to perpetuate the cycle. Several of the leading Venthyr are ‘sired’ directly by Denathrius, while the majority are instead transformed by lesser Venthyr. Their sinstones are then stored away as a relic of their past lives. Some of the leading Venthyr are granted a portion of Denathrius power through talismans that allow them to break the thought/reality barrier a little and grant them greater control over Revendreth itself.
What we learn, however, is that this process is not perfect, and what is considered appropriate penance is dictated by the Venthyr overseeing each soul. A Venthyr can champion for a soul they think has earned redemption to end their torment early, or, more often, a soul is judged at a rather arbitrary time whether they have achieved penance or are irredeemable, making Revendreth very political. During this process, they are ceremonially renamed.
Because these Venthyr, unlike the Kyrians, maintain a memory of their past life, we discover they are embarrassed by the sins stored on their sinstone and there is a bit of power behind knowing the ‘true name’ of the Venthyr. Because of this psychosomatic link, knowing the sins of the Venthyr and calling them on it and by their true name appears to allow one to have magical power over them. For some, however, that have truly moved on from their original sins, the sinstones have no real power.
Also, they do acknowledge a couple of times in the zone and story that some Venthyr do need to be sent back for re-evaluation if they begin to exhibit their old sins, however I get the impression this is more a political decision. Similarly, this does not prevent the soul from committing brand new sins as a Venthyr. It seems that specifically Avarice and Gluttony are permitted as a ‘lesser sin’ among the Venthyr as a way to keep them in line - if they are encouraged to dump all their sin into one pool, it is less likely they will commit offenses that may hurt the souls in their care.
Vampire to Venthyr Lore - Lesser Spoilers
While the Venthyr aren't Vampires that drink blood, they do have an anima dependency, and their flavor of anima is cherry. They don't have the moving water/garlic/holy symbol allergies, however they do respond to emotional attacks against their old selves. The coffin/crypt motif is actually a form of sensory deprivation torture for the souls.
The Shadowlands does need Anima to function, and it appears that for this specific afterlife to work, it does depend on the existence of evil.
The Light in Revendreth - Moderate Spoiler
We discover that much like the Void launching an attack into Bastion a long time ago, the Light launched a more 'subtle' attack into Revendreth. Bastion recovered from the void, a portion of Revendreth remains inhospitable to the Venthyr due to the ever-present burning light.
Whether normal sunlight would burn the Venthyr is unknown, however this 'L’ight does. Another interesting question is whether souls from other regions would burn here, or if its just a peculiarity of the Venthyr and the Lights philosophical disagreement with Denathrius.