The end of Giovanni's reprise of "Everything Changes," while cool on the soundtrack, is awesome on stage due to the helicopter sounds.
Team Rocket finally captured Pikachu and delivered him to Giovanni.
They were sent to capture Ash when Pikachu wouldn't obey their commands, but when Ash learned what happened to Pikachu, he ordered them to take him to Giovanni.
James tells Pikachu to "do that thunder thing you always do to us." He does, and shocks every Rocket in the room and frees Delia and Professor Oak.
When Giovanni says Delia made a big mistake when she walked out on him, Ash responds that it wasn't as big a mistake he made by stealing his Pikachu.
While the Pokemon battle between Ash and Giovanni is short, it was the closest they'd come to a fight until the Best Wishes anime series 13 years later—and in the anime, their fight was even shorter.
When MechaMew2 defeats Pikachu, Ash tries to fight Giovanni himself. With his fists. In song. Giovanni responds in kind.
Giovanni: Thank you, Ash Ketchum from Pallet Town! Now nothing can stop me! Ash:[charges forward, fists raised] I can, and I will! [cue "You Just Can't Win" as Rocket Grunts surround Ash]
During the fight, Giovanni tries to punch Ash, who dodges and taunts him about it.
Ash: Guess you're slowin' down, old man; can't hit what you can't catch!
Later in the fight, Giovanni grabs Ash by the chin/neck, lifts his head and shoves him away, then goes into a Badass Arm-Fold.
Giovanni tries to just kill Ash and Pikachu with Hyper Beam after they served their purpose in his plan. If not for Mewtwo's intervention, he would have won.
Mewtwo defeating MechaMew2 by teaching it compassion, courtesy of Ash's memories and pure heart.
MechaMew2 gains sentience and learns right from wrong, puts Giovanni in a headlock, and gives a touching speech just before blowing itself up.
Giovanni: I didn't give you the power of speech! MechaMew2: You didn't give me a lot of things, but you did give me the ability to learn. And I have. From the boy, I've learned about love and goodness. His heart is pure. His love for Pokemon and his friends and family is real. I've learned right from wrong, and I've learned which one you are. Now I know what I must do. Something else I learned... Self Destruct.
Giovanni gets some points for actually surviving the attack.