Green Dragonstones are alike in color with brilliant, deep emeralds, but shot through with a veinwork of fine golden threads. These burn with a bright golden light when the stone’s powers are activated, causing the entire gem to shine with a warm greenish-gold light.
Green dragonstones are closely tied to the Element of Water, and the Sphere of Time. Their power draws from the user’s Wisdom and lifespan.
Passive Powers: The user gains resistance against cold damage, as the Protection from Energy spell. The user can also breathe water. Both of these effects last as long as the stone is worn against bare skin.
Active Powers (Common):
This effect manifests as the Shape Water cantrip from the Elemental Evil Player’s Guide.
This effect manifests as either the Create Water or Purify Food and Drink spells.
This effect manifests as the Prestidigitation cantrip.
Active Powers (Uncommon)
Obscuring Mists (DC 13) (1st)
This effect manifests as the 1st level spell Fog Cloud.
Tides of Time (DC 13) (3rd)
The user can warp the flow of time around his or herself, an ally, or 1d4 opponents, with effects equivalent to either the Haste or Slow spells.
Master of Waves (DC 15) (4th)
A more powerful invocation of the Curent power, this ability allows the user to impose his or her will upon larger bodies of water, as outlined in the 4th level Control Water spell.
Active Powers (Rare):
Ice Storm (DC15) (4rd)
This effect manifests as the 4th level spell of the same name.
Polymorph Another (DC15) (4rd)
This effect manifests as the 4th level Polymorph spell.
Active Powers (Very Rare):
Disintegrate (DC 19) (6th)
This power accelerates the flow of time against its target in one large surge, reducing it to fine gray dust to which all matter eventually decays, if it fails a Constitution Save modified by the stone wielder’s Wisdom bonus.
Major Transformation (DC17) (6rd)
This effect allows the user to fashion an existing item into something to which it might eventually become, bridging the gap in time between in an instant. It can also be used in reverse, reverting an item of a weight equivalent to the carrying capacity of the user into its component parts. It cannot be used against creatures.
There are rumors that green dragonstones of legendary quality (such as Zirchev’s Viridian Eye of Time) allow the user to completely halt the flow of time, unravel all but the strongest of magics, or assume the true shape of any type of creature they have encountered.
Green dragonstones gain their powers from the wills of their users, aging the user a number of months equal to the effect's given level. If the user fails the activation Wisdom saving throw, the invoked effect ages the user a number of years equal to the equivalent spell level plus the amount by which they failed their Save.
Sirens can use a green dragonstone to slip into a temporary insubstantial state, assuming a gaseous form (as the spell of the same name). This can be done only once per long rest.
Shrikes can use a green dragonstone to rime their weapon in ice, dealing an extra 1d8 (d12 for fire-based opponents) points of damage to a target on a successful hit. When using an Andahar’s Edge in Archer-mode, the Shrike can manifest bolts of ice if she is out of ammunition, dealing 1d8 points of cold damage. This effect only lasts for a single combat, but can be used again after a short or long rest.
Sources: D&D Basic Rules, Players Handbook, Elemental Evil Player’s Companion.