Flames of Change or Offerings to Dahz
From RoR Wiki
Flames of Change is a quest from the Cultist of Flames during the Feast of Shoika.
The quest states that you should kill Kislevite Bulls.
Tip: It's advisable to take this quest before undertaking to complete the "Slay 30 Kislev Bulls" Task for the Feast of Shoika Live Event so that you can complete both at once.