Chen Shan showed no surprise when Swampert appeared, despite its moves being four times as effective against Aggron. He had anticipated this situation long ago.
"Aggron isn't that easy to counter." As Chen Shan spoke, he took out an Evolution Crystal containing pure Steel-type energy.
"Aggron, Mega Evolve!"
Chen Shan used Mega Evolution on Aggron, and powerful Steel-type energy erupted from the crystal and poured into Aggron's body.
Empowered by this energy, Aggron grew larger, and all its stats increased as it Mega Evolved into Mega Aggron.
After evolving into Mega Aggron, its original Rock and Steel typing became pure Steel.
With its typing reduced to Steel alone, Ground-type and Fighting-type moves that had previously been four times super effective against Aggron now dealt only twice the damage.
Chen Shan's battle commands were meticulous. He had not immediately Mega Evolved Aggron against Pidgeot because Mega Aggron would lose its Rock typing.
First, Chen Shan had used Aggron's Rock-type bonus to defeat Pidgeot, then waited until Swampert entered the battle before Mega Evolving Aggron.
As a pure Steel type, Mega Aggron no longer had as much to fear from Swampert's Ground-type moves.
"Mega Aggron, use Iron Tail!"
Chen Shan ordered Mega Aggron to attack with a Steel-type move it excelled at.
Swampert resisted Steel-type moves, but Mega Aggron's Physical Attack was high. With the boosts from its Metal Coat and same-type attack bonus, its Steel-type moves could still deal heavy damage.
Moreover, Steel-type Pokémon could not become poisoned, so Swampert had no way to employ its Toxic strategy.
Upon receiving Chen Shan's command, Mega Aggron sharply twisted its body and whipped its iron tail toward Swampert.
Powerful Steel-type energy gathered around its iron tail, giving it a distinctly dangerous air.
"Swampert, use Wide Guard!"
Zhang Cheng chose to test Aggron's attack