Lord Pumpkin is the Halloween Event boss, he has many devastating abilities, and summoning Soul Fetchers is among one of them. His arena can be described as a hellish cavern residing in the void, full of lava and other random fortifications.
Lavawave - This only affects the lower platform and kills most of the players as they camp near the ammo box located there
Exploding fireballs - The aiming is as poor as a firebreather's spit because it does not re-adjust and only shoots in the direction it is looking
Spawn minions - Summons Soul Fetchers to drag you into the lava occasionally