Pitbull’s Fireball needs to be playing instrumental/karaoke style in the background. Quiet at first, getting louder the closer they get to the main room of the cavern.
The various rooms leading into the main room are scattered with dead, unconscious, or barely conscious kobolds and goblins (a check of the living will tell they are deeply intoxicated or under the influence of something, likely a powerful drug. A check of the dead shows a 50/50 split between violent death and apparent OD).
Kobolds, goblins, and other assorted ‘minor’ villainous types are dancing in a conga line around a ‘treasure’ trove of mostly shiny looking junk and baubles. The treasure appears to be on fire, the flames are a whole rainbow of reds, blues, greens, purples, and yellows, flickering and dancing to the beat of music. Hovering two feet above the pile of treasures is a crystal about 3ft tall, glowing dim white and pulsing with streaks of opalescent rainbow colors to the music.
The music is performed by a diverse and raggedy group similar to those in the lines. Scattered around the room are the bodies of mostly kobolds and goblins.
Occasionally a fireball with materialize from the hovering crystal and land in a random part of the room, killing or roasting whatever happens to be there. A cloud will be released from the epicenter of the explosion and disperse around the room, adding to the haze. This cloud is what causes the intoxication. (roll a medium/hard Con check against. A fail results in a 50/50 roll. Result A means the character falls into blissful partying trance with the rest of the partying creatures. Result B means the character has a deep yearning desire to go and round up more ‘silly little creatures’ and bring them back to this neverending party.)
Why is this happening? It can be for whatever reason you find that fits best with the campaign.