Mallow had Steenee and Moon's Pokémon help them in the search for Mirage Berry. Steenee and the Pokémon asked of the wild Pokémon for the berries, which they accumulated. Later, Steenee was sent to battle Team Skull grunts, who assaulted Kiawe. Mallow continued fighting the Team Skull grunts. She had Steenee use Stomp to prevent the enemy from attacking Sun, Moon and Kiawe. Mallow sent Steenee to support Aether Foundation employees at battling Team Skull grunts.
Mallow's Steenee participated in the battle against the mysterious creatures, named Ultra Beasts, that Guzma sent to attack at Po Town. It fought an alluring Ultra Beast, but was wounded in the battle.
Mallow and Tsareena spent time on Exeggutor Island for training, and battled against Kiawe and Marowak. With the arrival of the four Guardian Deities on Poni Island, Mallow went out of the aircraft and started to battle the Ultra Beasts. She confronted Pheromosa, and had her Tsareena use Stomp, Trop Kick and High Jump Kick to hit Pheromosa. Next, Mallow passed the Z-Power onto her Tsareena, having her use Bloom Doom, which defeated Pheromosa.