Jester Thomas is an NPC in Dark Souls 2
Jester Thomas Information
An NPC Phantom that can be summoned for the Mytha, the Baneful Queen fight at the end of Earthen Peak which he can easily solo, even on higher NG+ difficulties as he uses the Forbidden Sun and Flame Swathe pyromancies to great effect (with unlimited uses). his Summon sign is right before the two Grave Wardens on the right of the staircase where the pool of poison was. (or is if you haven't burned the windmill) He uses dual Pyromancy Flames and the Jester's Set.
When going through Dragon's Sanctum he will invade just before the fog gate leading to the Lair of the Imperfect bonfire. He can be noted doing the ¨This One's Me¨ gesture and then will proceed to attack.
Earthen Peak. Near the staircase guarded by two Grave Wardens before Mytha's fog wall. His summon sign is submerged in poison if you haven't burned the windmill.
Dragon's Sanctum. He will invade the player in the Dragon's Sanctum, just before the fog wall to the Lair of the Imperfect.