The Crystalsmith appears to be a dark elf with crystals embedded in his face and a glowing crystal sword. His name is Shugi de Kurisutaru (Source, Anyasha).
He is crazy, and has been seen talking to walls, people who weren't there, and other inanimate objects that (presumably) didn't have spirits in them. This can be advantageous, because he sometimes drops useful information in his ranting. He may also switch randomly from talking to attacking, so be careful. He hates dark elves and will kill them if given a chance.
He is immune to death spells, and if you attempt to killing blow him, a wave of corruption comes out of his form, usually killing the person who attempted to kill him, and healing him at the same time. He is harmed by the spell 'purify blood', but also can taint your blood with a touch, so you probably want to save your purify blood spells.
He can also corrupt transforms within a very short period of time and no components.
Voidheart said once that he was crazy before he became Voidheart's minion.
He hates other dark elves and spends a good deal of his time hunting them down and murdering them.