Nikolaus rips open it's neck, to the point its' head is now more dangling off then attached. The Beast takes quite a few steps backwards, some how still barely alive, due to the Plague's affects on a person. It then falls to its' knees, a final death gurgle before it falls down completely. The impact severs the final connections of its' own head, making it roll away... 

Suddenly, the skin of the Beast begins dissolving ever so slowly, and memories of Joshua can be heard in everyone's minds. "If a Beast was using a lot of that weird fluid... it's highly likely it'll shower you with it when it dies. It'd be best to run away when you kill one." Oh hell, it's going to explode! Everyone runs as fast as they can, towards Joshua's camp. A very notable fizzle is sensed before the creature's body finally ruptures, and a sound not unlike that of someone puking, but much louder is heard. The Hunters look back, and it seems they thankfully just got out of the blast radius, puddles of that bile dissolving everything from grass to the exterior of trees in the area. Since it was a fairly large clearing, it didn't harm too much, which is decent.

It's then fairly obvious you all should [i]probably[/i] tell Joshua that you almost died from a Plagued Harpy revealing itself, fighting, then exploding.