Vanyver

Vanyvers are large, humanoid bats shaped from void and shadowstuff, their red eyes glowing like tiny stars in an otherwise lightless night. Though powerful, they're the least of the darvakkas, and the most likely to submit to a master, either another of their kind or a mortal with a reputation for being especially murderous and destructive. Vanyvers agree to follow their masters as a temporary means of maximizing the death and destruction they can enact but will quickly turn on any master they feel falters in this goal.

Darvakkas, also called nightshades, are a ravenous evil made up of equal parts darkness and malice. Originally creatures of the Outer Planes who travel to the convergence of the Shadow Plane and the Void—where the power of nothingness obliterates them—these undead abominations are the physical embodiment of entropy. They burn with an intense hatred for all life, working to bring a final, dark night to the Material Plane where nothing but ash and ice remain.

As creatures twisted by darkness and shadow, darvakkas have a great aversion to sunlight and all sources of vitality energy. On the Material Plane, they spend the hours of daylight hidden below ground, amid ruins, or submerged deep in the ocean's darkest chasms beyond the reach of the sun's rays, emerging when darkness shelters them overhead.

Darvakkas have an aura of entropy that attracts undead thralls to serve as warriors and heralds. They rarely seek alliances with each other or other creatures, existing in solitude as the heads of individual armies of the dead.