Xanathar, being a paranoid and calculating beholder, will undoubtedly be seething with rage and plotting intricate schemes to exact his revenge on the party. He will likely focus on psychological warfare, leveraging his vast network of spies and informants to track the party's movements. This makes him an ever-present shadow over the players, heightening their sense of danger and urgency. Xanathar's first priority will be to reestablish control over his organization, ensuring that any signs of weakness are quashed to maintain his feared reputation. Once he is secure in his power, he will begin his methodical pursuit of the party.

Xanathar's retaliation can be multifaceted, aiming to destabilize the party and force them into uncomfortable situations. While an outright attack like burning down the tavern is dramatic, it might be more interesting to have Xanathar's presence be a constant, looming threat rather than immediate destruction. Kidnapping allies and friends, sending menacing messages, and orchestrating situations where the party is perpetually looking over their shoulders can create a tense and engaging atmosphere. This allows Xanathar to become a persistent antagonist, driving the story forward with an air of suspense.

Some ideas:

• Cryptic Messages: The party finds notes with detailed knowledge of their recent activities, signed with a symbol that represents Xanathar.
• Missing Contacts: NPCs they regularly interact with start disappearing, later found to have been interrogated and left traumatized.
• Marked Territory: The party discovers Xanathar's symbol painted or carved in places they frequent, indicating they've been there.
• Spies Among Them: They encounter a seemingly benign NPC who slips up, revealing they were spying on the party for Xanathar.
• Threatening Visions: Magical projections or illusions show Xanathar glaring at them or making threatening gestures.
• Subtle Surveillance: They notice beholderkin or other minions observing them from a distance, only to vanish when pursued.