Stellium Guide

Stellium can be used to purchase various items from the Coin Reward Officer. Stelliums are obtained through Altar Siege and from Demaha weekly quests, and PvP rewards.
To go to Demaha, use the teleporter from Lakrum, and teleporter NPC in Sanctum and Pandaemonium.

Spoiler: Elyos

Spoiler: Asmodian

Stellium coin can used to purchase scrolls, designs, accessories, consumables and upgrading materials.

Spoiler: Asmodian NPC name Psykhe

Spoiler: Elyos NPC name Lorona

Spoiler: Altar NPC Mayoria Asmodian

Spoiler: Altar NPC Phlea Elyos

Phlea and Mayoria NPC are to be found in Demaha Altars
The NPC will show up after one of the factions successfully conquerors the Altar.
Stellium can also be used as a scroll which gives 150 PvP Attack for 10m.

Spoiler: Stellium Buff

For more info click this Link
To find the npc type /where name​