Demonfeed spider

Demonfeed spiders are the offsprings of giant spiders, spawned by the Spider Queen before the Calamity and, consuming the ichor of the demons fallen during the Great War, has transformed into spiders fiendish in nature.

Description
Unlike most fiends that are simply banished to their home plane when killed on the Material Plane, once demonfeed spiders are slain, they are slain forever. These spiders feed on the fluids living creature, liking to regale on the ichor that remains behind a demon slain on the Material Plane. When the poison of spiders mixed with the ichor, it becomes expecially potent, excreting from its chitinous hide when the hide is pierced.

Abilities
Demonfeed spiders and demonfeed spiderlings are resistant to cold, fire, lightning damage and immune to poison damage and poisoned condition. They also can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check, and ignore movement restrictions caused by webbing. In addition to the forementioned, demonfeed spidelings can only bite its target with less chance to hit and dealing less damage.

must make a DC 14 Constitution saving throw. On a failed save, a creature takes 13 (3d8) poison damage and is poisoned for 1 minute. On a successful save, the creature takes half as much damage and isn’t poisoned. If this poison damage reduces a creature to 0 hit points, the creature is stable but poisoned for 1 hour, even after regaining hit points, and is paralyzed while poisoned in this way.
 * Multiattack: The spider makes two melee attacks: one with its bite, dealing piercing and poison damage, and one with its stinger, dealing piercing damage and paralyzing the target if they fail a Constitution save; or the spider can make a melee attack followed by one ranged attack with its web spinner, pulling the target 40 feet toward the spider and grappling it (escape DC 14). The spider can grapple only one creature at a time in this way. As an action, the spider can cocoon a creature it has grappled in webbing, causing it to be restrained and ending the grappled condition.
 * Arterial Spray: As a reaction, when the spider takes damage while below half its hit point maximum, it can spray poisonous blood in a 15-foot cone. Each creature in the area

Known demonfeed spiders
The Mighty Nein encountered and fought nine giant wolf spiders and one demonfeed spider in the collapsed room of the King's Cage.

In Demonblood Vengeance adventure hook from Tal'Dorei Campaign Setting Reborn took place in 836 PD, after the death of a marilith disguised as a human named Iselda on the outskirts of Stilben, her ichor has spawned a brood of demonfeed spiders that now view her as their mother.

In Blood of the Ruiner adventure hook from Tal'Dorei Campaign Setting Reborn took place in 836 PD, the Ravagers of the Bramblewood Forest transformed a number of giant spiders endemic to the Bramblewood into demonfeed spiders through the blood ritual of the Ruiner.