Gurkinn was teaching his students the power of Mega Evolution when he was approached by Korrina in the past, who accomplished her tasks Gurkinn gave to her.
Gurkinn faced Essentia, who used Phantump in the battle. Gurkinn Mega Evolved Heracross, who started attacking Phantump. Since they had to run away from Essentia, Mega Heracross started attacking the roots with Korrina's Mega Lucario. Since they had to protect the secret of Mega Evolution, Gurkinn's Mega Heracross and Korrina's Mega Lucario launched Pin Missile and Aura Sphere to destroy the Mega Lucario statue to let the whole tower crumble.
Gurkinn battled Chalmers' Skrelp with his Mega Heracross. However, he failed and was pushed into the water, along with Mega Heracross, by the Skrelp, who tried to drown and poison them. Fortunately, Diantha and Gardevoir pulled them out of the water. Facing a thief, Gurkinn sent Heracross to battle the thief's Binacle, along with Diantha's Gardevoir and Korrina's Lucario. Since they were facing Binacle, who used two of their heads at once, Gurkinn Mega Evolved his Heracross. Once the thief took Diancie's diamonds, Gurkinn's Mega Heracross chased him off with Bullet Seed. Malva spoke to Celosia and recalled Gurkinn and Korrina, as well as their Heracross and Lucario, who fled the Tower of Mastery some days ago.
Heracross helped Gurkinn come to the battlefield, where everyone was fighting to take control of Xerneas tree. Heracross was present during Gurkinn's special training with Tierno, Shauna, Trevor and Y.
While explaining the situation to Blue, Diantha remembered running away with Gurkinn, his Heracross and Korrina, to find Yveltal's cocoon.