1. Entei, Raikou, and Suicune:
- These three legendary beasts roam randomly across Johto. You'll need to track them down using the Pokédex or Radio Tower reports and battle them to catch them.
2. Ho-Oh:
- You can encounter Ho-Oh at the top of Tin Tower after defeating the Elite Four and becoming the new Pokémon Champion.
3. Lugia:
- Lugia can be found at the Whirl Islands after you get the Silver Wing from Ecruteak City's Elder. Use the Silver Wing on the pedestal at the Whirl Islands to summon Lugia.
4. Mewtwo:
- Mewtwo is located in Cerulean Cave. You'll need the key given to you by Bill's grandfather in Goldenrod City to access the cave.
5. Celebi:
- To catch Celebi, you'll need to complete the GS Ball quest. The quest starts after obtaining access to the Johto Safari Zone. It involves interacting with NPCs, competing in the Bug-Catching Contest, and following clues to obtain the GS Ball. Once you have the GS Ball, return to Ilex Forest Shrine to encounter and catch Celebi.
Note: Some legendary Pokémon may require specific in-game events or items to encounter or catch them. Consult a detailed walkthrough or guide for additional details and requirements.