I've had the following scene prepared since the beginning of this battle, and I figure I might as well share it now because I have forgotten what arbitrary conditions I was waiting on before doing this reveal. So @Skullduggery, if you ever come back and decide you want to finish this fight, Arthur and Pakter will have their stats fully restored (including your metalminds), and they'll be up against this...
Suddenly, the two combatants hear a scream. Both Pakter and Arthur look towards the source: it’s the shepherd from earlier. It looks like one of his sheep is biting him on the leg. As they watch, the shepherd tries to beat the sheep off of him with his crook, and finally the sheep lets go. However, now all the other sheep seem to be moving towards him…
The ground ripples beneath the small flock, and then surges upwards in an explosion of grass, dirt, and rocks. The dust settles, and where before there had been a half-dozen sheep, now there’s a gigantic, misshapen form advancing on the shepherd. The bulk of the creature’s body is a jumble of translucent muscles, twisted spines and rib cages, and the skulls of a variety of animals—including at least one human skull. Looking closely, Arthur and Pakter can see several woolly shapes rising from the monster’s back, connected to the rest of the body by their hooves—this thing had disguised itself as the flock of sheep!
The skulls on the beast’s body open their mouths and start screeching all at once, an otherworldly cacophony of howls, bellows, and piercing whistles. The call splits the air, pounding on the eardrums of all who can hear it.
It’s a monster-wraith, and it’s ready to hunt.
The shepherd scrambles back awkwardly, half-paralyzed with fear. The monster-wraith surges forward and a rib cage at the front of its body opens wide like the maw of… well, like the maw of a monster. The tips of the ribs are jagged and sharp, probably from years of the monster-wraith using them as teeth. At the same time, a long muscular appendage reaches for the shepherd. The “arm” looks like an immensely strong human arm that has far too many joints, not to mention too many clawed fingers at the end of it.
The shepherd is keeping its attention for now, but one way or another that won't last long. Arthur and Pakter both realize that the monster-wraith will soon turn upon them, and if they don't work together, it's doubtful that either will survive.
And that's the "mysterious third party" we talked about when planning this arena battle. Voila!
The Arena itself, all duels take place here.