Eternal of Spring
Most commonly, Arhallogen is called the Spider King (although gender has little meaning for this powerful creature, it is usually addressed by male honorifics).
It is also occasionally referred to by other eternals by a name that sounds like a sequence of quick clicking noises - noises commonly produced by Arhallogen, its heralds and its spawn.
A swarm of poisonous insects and arachnids that speak with a single whispering voice; a monstrous spider-like, scorpion-like horror, all pincers and deadly stingers; or sometimes an insect-like vaguely-humanoid shape in cobweb robes and an iron crown, bearing a poisoned glaive.
Arhallogen is an inhabitant of the Spring Realm, and part of the family of eternals that are the most alien to humanity. It seems to be fascinated by the ways living things prey on and compete with each other, especially the adaptations and natural qualities that let them hunt, kill and consume prey - or that let the prey fight off their predators.
Unsurprisingly, the Spider King rates venom as one of the most potent tools that any living creature can employ, and is delighted to encounter new poisons.
During the Winter Solstice 378YE, Arhallogen was declared to have the enmity of the Imperial Conclave. The enmity was later removed, but not before the eternal launched a vicious attack on the Hall of the Worlds with venomous heralds.
This dark eternal encourages competition between living things, not so much out of a desire to see death or conflict but apparently from an urge to see living things survive and prosper. It offers a number of boons, many of them violent, and often involved with crushing weaker prey or poisoning stronger creatures to make them weak.
It lends its power directly to the ritual Fire in the Blood, an enchantment that grants increased ability to wield Spring magic, especially where venom is involved. It is known to favour the entire suite of Spring rituals that envenom opponents from Touch of Vile Humours all the way up to Fetid Breath of Teeming Plague and beyond. The Spider King is also reported to offer its power directly to rituals that create magical venom or poison, and there are stories of sinister curses that go beyond even the Curse of Gangrenous Flesh in their lethality.
In addition to attacks that kill, or envenom, Arhallogen also favours more subtle magic. The staff known as the Caress of Arhallogen allows the wielder to paralyse their opponents, and some scholars believe that the knowledge of how to make these magical implements was first derived from this eternal. Likewise, those who enjoy his favour have demonstrated the ability to entangle their foes to prevent them escaping. Neither effect is commonly associated with Spring magic, but heralds and agents of Arhallogen often wield implements that allow these powers to be employed.