Condensed Stygia

Condensed Stygia is an item that grants its user 250 stygia.

Source
It can be obtained through the following covenant table missions:
 * Coalescing Stygia
 * Dark Skies, Darker Prospects
 * Grandiose Designs
 * Maw: Breach the Planes
 * Maw: Coalescing Stygia
 * Maw: Ghelak's Revenge
 * Maw: Topple the Giants
 * Topple the Giants

Condensed Stygia is also a reward option available from the Great Vault. Characters that have completed a Mythic+ dungeon the week prior can choose it if none of their gear rewards are desirable. It is rewarded in stacks of 3, giving a total payout of 750 stygia.