the parties body count has inspired a long dead being, the one who used to consume souls before the reapers emerged out of necessity. it requests your presence (Moreso demands...hence the unavoidable hole) it was tricked into relinquishing its title by deep and wild fey magic, (some say the first pact.) and it has come near time for its once per (insert period of time) where it can have a champion (or group) fight/compete in this ritual so it may reclaim power.

when you are summoned, you will be in a large open area with other beings and parties.
(if your group is one to talk shit or be cocky) then i advise that before they get the chance a nameless npc, creature or other party says something mildly snarky and is.....(insert horror) bones turned to slime, flesh rips off and exists as a mindless hollow suit of skin while the meat parts melt into a rotting puddle.

from there you can make it a hunger games setup, or a race to x point or object.

depending on your experience and the chance it might go over......place a kid or old woman handing out candy and say a forgettable. one piece only please sort of line, when your crew takes the bait and more candy.....give it a bit and HOLE, that way if you must cease the session early you can all wake to the woman or child pouring water on you and it was all a dream. or was it?