Instructions
Defeating every gym leader in Johto and earn eight Johto badges. Get a second set of eight badges by beating the Pokemon of the eight gym leaders in Kanto. You should now have 16 badges in total. Speak to Professor Oak and he will give you access to Mt. Silver.
Purchase 30 to 50 Ultra balls at any PokeMart. Buy items that will restore the hitpoints of your Pokemon, such as Lemonade, and items that cure status effects like burns and paralysis. If you don't enjoy battling wild Pokemon, buy Repels, as well.
Place three to four Pokemon that are around level 50 in your party. Teach these Pokemon moves such as Surf, Earthquake and Hydro Pump. Moltres, a Fire type, is very susceptible to Water and Ground type moves.
Travel to Mt. Silver, which is located to the left of Viridian City. Enter Mt. Silver and you will come across two barriers that you can cross by using Hidden Moves. Instead of using HM 08 to climb the rocks, use HM 03 to get across the large body of water.
Travel to the bottom of the cave by following the path and by using the various ladders. You will need to use multiple HMs if you want to reach Moltres. Once you reach the very bottom of Mt. Silver, you will see Moltres. Save your game before you go to battle.