Instructions
Catch a Yanma, or trade one of your Pokemon with another player for it. In SoulSilver, Yanma is a wild Pokemon that will appear in random battles on Route 35. However, you have only a 1 percent chance of seeing it by relying on luck alone. Listen to Professor Oak's Pokemon Talk radio station in your PokeGear, and he will announce the different swarms of Pokemon spotted each day. When a swarm of Yanma are spotted, your chances of finding one increase to 40 percent.
Teach Yanma the Ancientpower attack. This can be done by raising Yanma to level 33 or taking it to the Move Tutor in the Frontier Front and paying him 40 Battle Points.
Level up your Yanma once it knows Ancientpower, and it will evolve into Yanmega.