The rules for a Drunk World Seed are a bit different than Vanilla Game, it relies on a good portion of Veteran knowledge to navigate.
In this specific instance, you're expected to battle with Skeletron underground, but if you're familiar with the Plantera fight, just treat this battle the same way. "The Old Man" should be located in a small room, off-to-the-side, somewhere inside the Dungeon, speak to him first during the Night, before going any lower into the Dungeon!
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