Who the Fuck is he?
Nethissil is an imp trying to cause corruption and gain control in EverShade. He found the House of Cards alchemist Carlos and tempted him with great power and wealth. Carlos was one of many Cards zealots manipulated by a league of devils.
When confronted by his coworker Laethin and the barely-formed party of PCs, Carlos lost his mind, jumping out of his apartment window. He landed, died, and burst into flames, his ashes poetically floating away on the wind.
Not much is known of Nethissil. He apparently had a strong influence on Carlos and may have convinced Carlso to create a monopolized market on Helena, the drug that he, Laethin, and the other alchemists at the House of Cards created.
Whoever he is, Nethissil must be intimidating. Carlos leaped to his death from his apartment window when he thought he might be betraying Nethissil.
During the fight in the house of cards, it was revealed that Nethissil is an imp. However, he was not the imp that we totally cut in half. Quell Domage.