I align my Shamans on the road facing the crypt and pull with my Paladin. Then I just brute force the horseman with Lightning Bolt. When the head drops, I manually target it (rather easy to follow because of it green vapor thing), then flame shock and lava burst it. I never seem to be able to finish it on the first time it detaches, though, but it goes down very quickly on the second time.

The only slight issue is when the head flies behind my Shamans. Then I do an "interact with target", put them back in formation and start DPSing again. Sometimes it takes a third detach to kill the head then.

Globally very easy with my current gear.