WoWDB

To add to what Simca has mentioned, do not kill the Loa Speaker.

You will also want to have the Loa-Infused Bloodhorn at least 15 yards away from the vase. The reason for this is because the direhorn will not charge with its  Trihorn Charge if you are within 15 yards of it. 

My group had the paladin and myself go tank and heals, respectively, to play it safe. That turned out to be the right call, as the Bloodhorn guy was a slowpoke and its  Triple Puncture stacks. Meanwhile... myself, Aliok, and the warrior stood by the vase since we weren't quite sure as to how the charge worked. We had also placed a world marker about 18 yards out to make sure no one would be too close to the direhorn.

In the end, it turned out that the charge only targets the person with the aggro. So when it began to cast its Charge, the tank ran over to where the rest of us had been standing. We watched as the vase spent a couple seconds wobbling and then got credit when it hit the ground.

At this point you can either kill the Loa Speaker or go invis. Don't bother hitting the direhorn - it'll turn friendly once you've killed its master.