In the Ultimatum League, you’ll have the option to complete 40 new challenges and earn exclusive microtransaction rewards. At 12, 24 and 36 challenges, you’ll earn the Ultimatum Helmet, Ultimatum Pet and the Ultimatum Portal respectively. Completing challenges also grants you pieces of the Ultimatum Totem Pole Hideout decoration.
24 Challenges Rewards: Ultimatum Pet
Path of Exile Ultimatum Challenge Rewards