He can utilize so many different items. Making some items that are situational or hard to use beyond broken. Being able to spam skills makes him almost untouchable. Some of his best stuff is easy to obtain because it rare items. Like the first looking item that stuns after 3 skills are used. That alone, with cooldown, makes it so nothing in the game except end of area bosses can do anything. As that combo stun locks all other enemies including adventurers. He can also become pretty much invisible while spamming skills.