This requires a Member Card that can be obtained via Nintendo Event. Speak to a green man at any Pokémon Center to get the Member Card. With this item, go to Canalave City and enter a house that was previously locked but now open. You may want to save your game before entering the house. A sailor will tell you that you’re about to have a nightmare and you’ll end up on Newmoon Island. Enter the forest where Darkrai is. Darkrai is on Level 40. It has an ability called Bad Dreams, which slightly damages sleeping opponents every turn. Darkrai has a combo using Hypnosis and Nightmare. Wait until night time and use Dusk Balls. After the battle, you’ll find yourself back at Canalave City. When Darkrai reaches Level 66, it will learn its signature move called Dark Void. Dark Void puts all opponents to sleep. ... https://www.youtube.com/watch?v=y6bw7vSl1sk

At Twist Mountain, there is a hidden cave in the basement of the mountain where you must use Strength to move boulders. After moving the boulders, you’ll see Regigigas. To awaken this Pokémon, you must have Regirock, Regice, and Registeel equipped in your team. Save your game before you interact. Regigigas is on Level 68. It has only half the Attack and Speed for the first 5 turns due to its Slow Start ability. Dusk Balls would be recommended since you’re battling in a cave. If Regigigas reaches Level 75, it learns Crush Grip, a move that does more damage the higher the target’s HP is. ... https://www.youtube.com/watch?v=H7vwMcJ1P-0

After returning a Machine Part to the Power Plant, get the Expn. Card from the director at the Radio Tower in Lavender Town. With the radio on PokéGear, tune into the Poké Flute channel while you’re in front of a sleeping Pokémon blocking the way. Save your game before you interact with it. Snorlax is on Level 50. Use Thief to steal the Leftovers it holds to prevent it from regenerating every turn. Snorlax will use Body Slam to paralyze opponents then Rollout that grows stronger every turn until 5 turns. If Snorlax is low on HP, it will use Rest. Heavy Balls would be the best choice to capture it. After the battle, enter Diglett’s Cave. ... https://www.youtube.com/watch?v=jUc3iPVAPro

This requires an Eon Ticket that can be obtained from a certain Nintendo Event. With the Eon Ticket, go to the shipyard in Lilycove City and the attendant will examine the ticket you have so you can be eligible to go to the Southern Island. At the Southern Island, save your game in front of the mysterious ball. Interact with the mysterious ball and Latias will arrive. Latias is on Level 50. Its signature move is Mist Ball, a move that will lower the target’s Special Attack stat 50% of the time when the move hits. Use Ultra Balls and status problems for a better capture result. Once you capture Latias, you’ll notice that it is holding a special item called Soul Dew. Soul Dew raises the Special Attack and Special Defense stats if held by Latias or Latios. ... https://www.youtube.com/watch?v=21C-1LxrnQA