Liam used the Pokedex.

"[i]Xerneas the Life Pokemon. Legends say it can share eternal life. It slept for a thousand years in the form of a tree before its revival.When the horns on its head shine in seven colors, it is said to be sharing everlasting life.,

Yevetal, the Destruction Pokemon. When this legendary Pokémon's wings and tail feathers spread wide and glow red, it absorbs the life force of living creatures. When its life comes to an end, it absorbs the life energy of every living thing and turns into a cocoon once more.[/i]"

Liam went up to Yevetal. The Destruction Pokemon was enraged and would not listen to reason. He fired an attack, which Liam dodged by some miracle. It blew a hole in the wall. It hit Lysandre's Gyarados who had turned to stone. The Megastone fell to the floor and rolled into the room, stopping at Liam's foot. Liam used the Master Ball to catch Yevetal. Yevetal tried for several minutes to break out of the ball. It finally stopped shaking after several minutes.