Called “night stones,” “light drinkers,” “shadow stones,” black dragonstones appear at first glance to be deep purplish opals or highly polished onyx. A closer look reveals their main crystal structure to be nearly black, shot through with veins and lattices of purple. These purplish veins glow when the stones’ powers are activated, but rather than shedding light, when the stones are “aglow,” they sometimes sap the radiance from nearby light sources.
Black dragonstones are closely tied to the Sphere of Entropy. Their power draws from the user’s Charisma.
Passive Powers: Necrotic resistance; checks to hide while in shadows or shadowy conditions have advantage; darkvision, 30’ (or an additional 30’ if the user already has it); natural lights’ radii dim by 5’ within 20’ of a black dragonstone. This increases by another 5’ when an active power is used.
Active Powers (Common):
[Silva] clenched her right hand into a fist, and the dark stone adorning her wrist ignited with a harsh purple-black radiance. The stone throbbed once, sending a burst of the light pulsing down tthe metalwork of the bracer with an angry hissing, sputtering sound.
The writhing energy raced up the length of the sword, and crawled up the guard’s hand and arm like so many scuttling, spitting spiders.
This effect manifests as the shocking grasp cantrip of the same name.
Active Powers (Uncommon)
Blind (DC 13)
This effect manifests as the 2nd level spell blindness.
Darkness (DC 13)
This effect manifests as the 2nd level spell of the same name.
Invisibility (DC 15)
Her panting became a squeal of surprise, her head snapping up, nearly tripping herself as she spun to face her attacker.
And promptly caught a face full of snowball.
She blinked, sputtering, and sat down hard in the snow.
“Gil-ya—” she started, and another snowball choked off her accusing cry.
As he laughed, and lobbed another, Silva winked out of sight.
This effect imperfectly mimics the 2nd level spell of the same name. Movement faster than a walking pace produces a rippling of the air around the individual (or group, see below), negating the disadvantage to attack rolls if the attacker makes a Wisdom(Perception) check at DC 15.
The user can extend the veil of invisibility to up to four more individuals so long as they remain in contact. The DC increases by +2 for each individual so linked.
Active Powers (Rare):
Obscure Trail (DC18)
She glowered at the tracks she’d made in the snow, then stuck her tongue out at the swordsman, and blinked back out of sight.
“I’ll still be able to see you,” he sang, and lobbed another few snowballs at the place where she’d disappeared.
They fell on empty space.
Gilliam’s smile faltered a bit, and he searched left and right, tossing and catching a snowball in one hand as his eyes swept the courtyard for signs of the girl’s passage.
This effect manifests as the 2nd level spell pass without a trace.
Call Lightning (DC 18)
She placed her right hand flat on the forest floor before her, and shouted “Jvalat!”
The bracer flared with blue-white light, and we felt a sharp jolt ripple through the ground.
Bargle regained his composure, snatching his hand from the girl’s grip, tugging the sleeve of his leather coat back into place.
“Dramatic, but hardly impressive,” he sniffed.
The ground jolted again, and one of the trees nearby burst apart in a flash of blue-white fire.
This effect manifests as the 3rd level spell of the same name.
Active Powers (Legendary):
Soulbind (DC 28)
The ogre took another lumbering step, a jerky motion to the side, revealing the girl standing behind it, her right arm outstretched, the wrappings about the gauntlet in tatters. The gem on her right wrist glowed with the blue-white-purple of moonlight and shadows, bright as a handful of candles. A hazy webbing of misty strands drifted from along the metallic tracery of the gauntlet, over her right hand, and trailed across the floor to somewhere along the ogre’s back.
This effect manifests as the 5th or 8th spells dominate person or monster.
Sirens can use black dragonstones to bind demonic essences, if the proper chord is sung. If the demon fails a Charisma save vs DC 15, it is absorbed and imprisoned in the stone. The DC increases by two for each additional siren singing a note within the chord's structure.
Shrikes are able to burn these stored essences’ Hit Dice to heal themselves or as fuel for effects that would normally consume the shrike’s own hit points.
Sources: D&D Basic Rules, Players Handbook.