A new supplement for Frostgrave is now open for pre-order. From the Osprey Games site description:

Frostgrave: Mortal enemies

Enhance your Frostgrave campaigns with recurring villains that grow more powerful over time and give your wizards somewhere to hide with expanded rules for bases.

On the violent and deadly streets of the Frozen City, feuds and vendettas are commonplace. Wizards may start out focused on discovery and exploration, fighting when necessary for survival or to win possession of some long-lost artefact or grimoire, but such battles can swiftly become intensely personal. Competitors become adversaries and, as the cycle of violence continues, some wizards lose sight of their original goals and focus their efforts on the elimination of their hated foes – their mortal enemies.

This supplement for Frostgrave: Fantasy Wargames in the Frozen City presents rules for creating recurring villains in both competitive and solo campaigns. These characters are unique individuals who return over the course of a campaign to plague the players’ wizards, gaining experience, recruiting allies, and becoming more deadly with each appearance. Against such threats, a wizard’s base becomes as much hideout as headquarters, and an expanded range of options for enhancing bases is provided, as are rules for defending your own… and attacking those of your rivals!

MSRP is $24 USD with release on March 28, 2024. Current availability seems to be digital only.