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The Giant Rock (Japanese: 巨石 Megalith) is an ancient, giant stone in the anime that contains massive amounts of Primal energy. It was used by Lysandre to create a Zygarde-like entity.
The Giant Rock in its Zygarde form
The Giant Rock first appeared in Mega Evolution Special II. Lysandre had his scientists research it, but Mega Rayquaza tried to attack them. Alain and Steven attempted to fend off the Sky High Pokémon, but the Giant Rock disappeared. During the events of Mega Evolution Special III, the super-ancient Pokémon battled over the Giant Rock, due to being attracted to its massive amount of Primal energy. While Alain and Steven fought off Groudon and Kyogre, Lysandre managed to secure the giant stone. During the events of Mega Evolution Special IV, Chespie got hurt saving Squishy from Team Flare, causing it to radiate energy and enter a comatose state.
After this, the Giant Rock made a brief appearance in Unlocking Some Respect!, where it was seen in Xerosic's lab. It did not have a major role until the events of Rocking Kalos Defenses!, where it was revealed that, in case Team Flare lost control of the two Zygarde, Lysandre had planned for it to absorb Chespie and transform into a copy of Zygarde, which would collide with the Anistar City Sundial and release enough energy to wipe out all life on the planet. It was created when Serena, Mairin, Professor Sycamore and Team Rocket invaded Lysandre Labs, destroying the laboratory during its conception and forcing all Team Flare agents present to flee. It could not be stopped by Ash, Alain, Steven, Serena and their strongest Pokémon, although Ash-Greninja was able to sense Chespie's presence in the giant creature and marked its location with a Water Shuriken.
During Forming a More Perfect Union!, the group was helped by Kalos Gym Leaders, Diantha, and Malva. Together, they all helped clear or destroy some of the Giant Rock's roots in order to pave the way for Ash, Alain and their Pokémon to enter the Giant Rock's inner core and rescue Chespie, which deprived the Giant Rock of its power source, thus rendering it inert. Lysandre ultimately had to personally power it back up using his control device, but in response Squishy and Z2 transformed into Zygarde Complete Forme, which was able to match Giant Rock in combat. Although Lysandre attempted to fight back, he was defeated when Ash's Greninja, Pikachu and Alain's Charizard destroyed his control device, allowing Zygarde to attack the Giant Rock with Extreme Speed, which made a massive hole in it. It was then destroyed with Squishy's and Z2's Core Enforcer, an act that seemingly killed Lysandre, although his ultimate fate was left unclear.
It appeared again in Till We Compete Again!, during a video fantasy and a flashback.
In its Zygarde form, the Giant Rock has roughly the same body shape as a Zygarde 50% Forme, except it is much larger. Its upper body is primarily made out of stone, with a glowing red crystal serving as its "eye", whereas its lower body is composed out of vines. These vines also serve as a defense mechanism to protect the core body from attacks.
The Giant Rock is partly hollow inside, with its "innards" being composed out of glowing red crystals, with Chespie, its power source, at the center. These red crystals will likewise grow and shift to serve as a defense mechanism for its energy source. Even after the power source is removed, Lysandre still managed to power it up remotely using a control device coupled to his gauntlet.
Due to its vast size and mindless nature, the Giant Rock is extremely difficult to slow down, let alone defeat. In order to stop it, Steven, Diantha, Ash, Alain, Malva and Professor Sycamore, as well as eight Kalos Gym Leaders, needed to have all their strongest Pokémon team up against it. Even then, after Lysandre powered it up again, Squishy and Z2 had to transform into Zygarde Complete Forme to stop it, and only managed to do so after Ash's Pikachu, Greninja, and Alain's Charizard destroyed Lysandre's control device.
- As a Zygarde, the Giant Rock's characteristics parallel those of the fake Groudon from Jirachi: Wish Maker. Both of them are artificial, corrupted, bigger versions of a Legendary Pokémon, created by characters associating with villainous teams whose goals were to capture and control the real version. Both creatures are also mindless beasts whose sole intentions are to absorb more power.
- The Giant Rock in its Zygarde form has a number of similarities with the ultimate weapon. Both are weapons powered by the energy of Pokémon channeled through special stones, are capable of firing catastrophically powerful laser beams, and are used by Lysandre in his bid to destroy and remake the world according to Team Flare's ideals only to have their power sources removed and ultimately be destroyed with Lysandre within them.
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