Legendary Arena Ultra Hard
3v1 Tapu Bulu with Empoleon-Serperior-Swanna team
For the sake of completeness, here’s an f2p option to beat the Tapu Bulu’s Legendary Arena. Serperior is so sustainable particularly for this battle due to its blood sucking strategy with Giga Drain, further compounded by the gradual heal resulted by Grass Terrain.