Pokémon : S5 | E55 – Mother of All Battles

As Ash and his friends continue towards the Mt. Silver Pokémon Preserve to return Larvitar to its home, they stop as Brock tries to catch his breath. Meanwhile, Misty marvels at Larvitar's improved confidence as the young Pokémon is happily being carried in Brock's arms. Brock is unable to read his guidebook's map for directions to the Preserve, though Larvitar leaps out of his arms and rushes over to a nearby rope bridge. The group follows, deciding that it's leading them to it birthplace. While everyone is crossing, a periscope rises from the water, watching them. On the other side, Larvitar is cheerier than usual as it guides everyone through a forested area. In the bushes, a mecha is hidden with the same periscope aimed at them. Inside are three men, who decide to steal Larvitar after spotting it walking passed.

The group stops walking after hearing some loud noises. The growls continue to get closer and the ground begins to shake, until a huge Pokémon appears in front of them. Ash holds up his Pokédex and learns that they have encountered a Tyranitar. The group notices a familiar scar on Tyranitar's chest, and realize that this must be the very Tyranitar they saw in Larvitar's dream. Brock declares that the Tyranitar must be Larvitar's mother. Tyranitar looks endearingly at her child. Unfortunately, she gets upset when Ash tries to push Larvitar forward and fires a Hyper Beam at the group. Brock realizes that she probably thinks they are the poachers. They run away, leaving Larvitar with its mother. Ash looks back and sees Larvitar crying and running behind them, despite Ash telling it to stay. Larvitar ignores the group’s pleas and grabs a hold of Pikachu’s tail. Tyranitar fires off another Hyper Beam as Ash and his friends continue to flee. Ash eventually drops Larvitar and Tyranitar looks at it curiously. Larvitar lets out a mighty Screech. Tyranitar suddenly realizes that Larvitar is her child and apologizes to Ash and his friends.
(Source: Bulbapedia)