As the lone remaining orc looks around, the thundering sound of feet grows louder and louder. Finally, an enormous creature appears at the edge of the battle.
It looks as if two giant spiders of different species were merged at the thorax, so that the mouth of each is facing in oppoisite directions. You can count at least ten spider legs. In front of each of the two spider mouths, where you would expect to see two legs, you see two arms instead, possibly taken from orcs or goblins. Each of the four arms carries a battleaxe.
At first, the legs of the aberrant spider beast appear unable to agree on a direction. When it spies the stone and the party, they at last agree, and begin rushing toward you. This thing is astonishingly fast, given its hacked-together nature.
The remaining orc snickers when the beast arrives, and moves behind the beast for cover. Unfortunately for the orc, the spider is apparently hungry, and quickly sets upon the orc, silencing its screams with hideous chomping noises.