This goblin is covered with glowing sigils that pulse with power. It can call into existence phantom blades to attack its foes.
A Goblin Conjurer has the ability tosummon swarms of spectral blades just like the Staff of conjuration. Spectral blades are quick, swarming, levitating enemies. When the conjurer is killed, any blades it summoned will disappear. Conjurers frequently appear in packs with other types of goblins and jackals.
Lead them into a corridor where they will summon the blades. If there are any blades behind it, the goblin will not be able to flee, and you can quickly dispatch it.
Be careful with this tactic, as the goblin conjurer can summon enough blades to hold you off without ever putting itself at risk.
Have it follow you up or down a staircase. A conjurer will pursue, but It's blades can't follow. If you're standing next to the stairs, you'll get at least two free hits in. If you still don't defeat him, you can use the stairs again, and the blades he left behind on the previous floor will vanish when you arrive.
Use a Wand of Beckoning to draw it close then attack it.
Use ranged attacks against it, and try to find gaps between blades.
Stand on the other side of a door. It will generally send a few waves of blades but will eventually come through to see what you're up to. Whack it.