Magic Items

In the event that Terry survives the adventure, he bestows on the party the opportunity to make a greater fey pact, offering either a Wish or a copy of his spell book (A Tome of Clear Thought).
Breaking the Pact:
In the event that a character fails to eat ice-cream as part of their morning meal for three days in a row, these benefits are lost, in the case of the Wish it is removed from the character, in the case of the tome, the book is rendered blank, and all knowledge gained is forgotten.

Wondrous item, rare
You can use an action to blow this horn. In response, warrior spirits from the plane of Ysgard appear within 60 feet of you. These spirits use the berserker statistics. They return to Ysgard after 1 hour or when they drop to 0 hit points. Once you use the horn, it can't be used again until 7 days have passed.
The silver horn summons 2d4 + 2 berserkers.
The berserkers are friendly to you and your companions and follow your commands.