@BillsomethingIn the tavern is a msg board, asking for the retrieval of some odd items conveniently located uniquely (and coincidently) within each realm of each different character.
They are important to the owner, (he might lie about the reason for them or there could be some deception or other parties along the way.)
But nonetheless as you collect more you realise their significance and growing power.
But once the items are collected he turns villain forcing the hero's to use it against him.
In the end he uses them to try kill himself, because like everything in the tavern, he too repairs with it. He just wanted it to end.
Upon his failings the item you gathered and created is taken and a true enemy emerges.
The power of the tavern is fragmented, you travel it's connecting worlds again (this time through time) learning of the enemy, the tavern and the owner as you chase to retrieve the threat you created.
Some timey whimey stuff happens,
Circle of life
All for a reason
Last Boss fight... Or is it?
But that's an overall driving plot that I was slowly trying to introduce here, within each world there is another story built around retrieving the item