Shadowseer

Shadowseers, known in the Eldar Lexicon as esdainn, are powerful Eldar Harlequin psykers whose abilities are centred around spreading confusion and fear during both a Harlequin performance or Masque and on the battlefield. During a Masque the Shadowseers of a Harlequin troupe act as the primary storytellers, releasing programmed hallucinations from their creidann grenade launcher backpacks which form scintillating phantoms that dance and duel in the air. In battle, they can force visions of unholy terror upon the foe, or even remove the recognition of the Harlequins' presence from their enemies' minds altogether. In older Imperial texts they are sometimes referred to as Harlequin Warlocks.

High Shadowseer
The High Shadowseer, sometimes referred to in older texts as the High Warlock and called in the Eldar Lexicon the athesdan, is the overall commander of a Harlequin masque's Shadowseers, and may overrule commands issued to Warlocks by their Troupe Masters -- though this rarely happens in practice. It is not unknown for a High Warlock to take the Warlocks from the troupes and form them into a separate unit under his (or her) own command. The High Shadowseer advises the High Troupe Master on all psychic matters pertaining to a masque. In performance, the High Shadowseer leads and coordinates the other Shadowseers as they play the role of a supporting chorus to his Storyteller; in battle, the High Shadowseer may coordinate the Shadowseers' grenade barrages, or act as a completely independent warrior.

Wargear
Harlequin Shadowseers generally rely on their psychic abilities to serve as their primary weapons, though they also make use of the creidann bckpack which can fire grenades that produce programmed hallucinations of mind-boggling terror in their foes. For ranged combat Shadowseers usually rely on Shuriken Pistols and on Eldar Power Weapons in melee.