Instructions
Capturing Entei and Raikou
Exit the nearest city to the closest route on either side. Entei and Raikou roam the entire Johto region, appearing in any place at any time. Check your PokeGear on the Nintendo DS's bottom screen for their current locations. Access HM Fly on your Pokemon's submenu to fly to Entei or Raikou's current location.
Open your menu on the bottom screen and select the "Bag" option. Choose the "Items" pocket and select the item "Repel." Repel prevents low level wild Pokemon from initiating battles. Walk through tall grass, periodically checking your PokeGear for either Pokemon's presence. Keep walking until you encounter Entei or Raikou.
Trap Entei or Raikou in battle with Pokemon moves that prevent wild Pokemon from fleeing, such as "Block" or "Mean Look." You can attempt to inflict the status "Sleep" on either Pokemon with the move "Hypnosis." Battle Entei and Raikou using Pokemon with type advantages --- Rock, Ground or Water for Entei, Ground for Raikou. Capture either using Ultra Balls or regular Pokeballs; using a Master Ball immediately captures Entei or Raikou during the start of battle.
Capturing Suicune
Exit Fuchsia City, heading northeast onto the dirt road. Continue into Route 15 and walk southeast, avoiding trainers and wild Pokemon along the way. Use Repels to ward away low level wild Pokemon. Continue east to Route 14 and head north to meet a lounging Suicune in the water.
Watch the scene that unfolds after Suicune leaves; Eusine, an avid Suicune admirer, starts a conversation with you. Fly to Cerulean City with your desired Pokemon's HM Fly; select the move from your Pokemon's submenu after selecting "Pokemon" from the main menu. Head northwest from Cerulean City's Pokemon Center onto the nugget bridge of Route 24. Continue walking east around a maze of trees to reach a house and cobblestone walkway leading to a set of stairs.
Ascend the stairs to trigger a scene with Suicune; as you approach Suicune, an exhausted Eusine runs into the scene, declaring you the "winner" of the chase. Approach Suicune, pressing the "A" button to initiate the long awaited battle. Grass and Electric Pokemon help weaken Suicune, due to their type advantage against it. Capture Suicune using Pokeballs, such as Ultra Balls, after its health whittles down to yellow or red.