Instructions
Proceed through the game until you're at the end of Mission 11. After a brief cutscene, you'll square off against Latios.
Draw a circle around Latios with your stylus. Avoid touching Latios himself or you'll get hurt. Every time you draw a circle around him, you cause damage to Latios. At first, he can't counterattack, but after reducing himself to half life, he starts to defend himself.
Avoid Latios while the three energy balls float around him. He causes a lot of damage while they guard him. After a few seconds, the energy balls will dissipate. Start drawing circles around him again.
Keep attacking and evading Latios until he's defeated. After the battle, you'll be able to call upon him by drawing his symbol on the touch screen.