Every few levels, the party encounters "scrying eyes" (magical cameras). Halaster provides comedic commentary, offers "prizes" for entertaining combat, and creates "commercial breaks" where the party is briefly safe but must endure his rambling.
Have another group of adventurers (the "fan favorites") descending at the same time. This creates a race for loot and a sense of a living world. WDotMM.rar
Chasing a legendary criminal who fled into the Yawning Portal. Every few levels, the party encounters "scrying eyes"
Arcturia and the Shadowdusks (Halaster's apprentices) are tired of his madness and are plotting to "modernize" Undermountain and use it to invade Waterdeep. This creates a race for loot and a sense of a living world
Investigating rumors of a lich (Halaster) amassing an army that threatens their deity’s domain. Quick Integration Tips
Halaster has grown bored over the millennia and has invited "contestants" from across the planes.
Many DMs recommend using the Dungeon of the Mad Mage Companion from DMsGuild, which provides a structured "Game Show" script for the entire campaign.