To unlock the legendary beast trio, you must go to Burned Tower and take the stairs down into the basement. There, all three beasts lie dormant. Approach them, and they will be revived and run away: Raikou takes off west, Entei takes off north, and Suicune takes off east. You will now be able to encounter the first two randomly on any route in Johto. As for Suicune, follow the Suicune and Eusine page for more details. Be careful though; these beasts are much harder to catch than any other legendary in the games. They will flee on their first turn of battle or try to Roar you away if you use a trapping move like Spider Web. Thankfully, all damage and status you inflict will be there next time you encounter them. Don't knock them out though - if you do, you'll ruin your chance at catching the respective dog and will have to trade them in from another game. It is recommended you use your Master Ball to catch whichever one you like best. Fast Balls also work well on these Pokemon.

#243 Raikou

Location: Johto

Method:
This Electric-type legendary is an excellent choice for battle. With only one weakness and a great Special Attack stat, Raikou is ready to inflict serious damage with moves like Crunch and Thunder. For an interesting combo, try using Rain Dance to summon a storm on the first turn, then hit with never-missing Thunders on subsequent turns.

Raikou
Level 40
OT:Yours
ID:Yours
Hold Item:
None
Leer
Thundershock
Roar
Quick Attack
#244 Entei

Location: Johto

Method:
The Fire-type Entei can be tricky to use. Although he has incredible HP and Attack, his physical move set is rather lacking and he cannot benefit from both his titanic power and his strong STAB move Fire Blast. Despite this, Entei does get moves like Iron Tail and Strength to dish out damage, and it doesn't have abysmal Attack. Entei gets Solarbeam so use that in conjunction with Sunny Day for decent coverage.

Entei
Level 40
OT:Yours
ID:Yours
Hold Item:
None
Leer
Ember
Roar
Fire Spin
#245 Suicune

Location: Tin Tower

Method:
An awesome bulky Water-type Pokemon with high HP and defenses. Suicune is great for whittling down tough foes with Toxic or Roaring them away for later, but with moves like Surf and Blizzard it can also function as an excellent fighter. This is the only chance to get one, but you don't have to worry about it fleeing from battle or using Roar to end the match. Make sure you catch it for what's next.

Suicune
Level 40
OT:Yours
ID:Yours
Hold Item:
None
Leer
Bubblebeam
Rain Dance
Gust

The legendary birds in these games have different methods of capture compared to those in the other two games. Both will be encountered after the Elite Four at Level 60.

#249 Lugia

Location: Whirl Islands

Method:
The Silver Wing is obtained from an old man in Pewter City after beating the Elite Four. Take it to the top right of the Whirl Islands and proceed on your way. Lugia has among the highest defenses in the game but can also function as an attacker due to its above average Attack and Special Attack stats. Try a Heavy Ball on it for an easier catch.

Lugia
Level 60
OT:Yours
ID:Yours
Hold Item:
None
Recover
Hydro Pump
Rain Dance
Gust
#250 Ho-Oh

Location: Tin Tower

Method:
The RainbowWing is obtained from Eusine after catching the three dogs and showing him in Celadon City. He will bring you to Tin Tower and allow you up the previously blocked stairway. Ho-oh always carries the Sacred Ash, which fully heals your entire party. Use it if you need it against Trainer Red.

Ho-Oh
Level 60
OT:Yours
ID:Yours
Hold Item:
Sacred Ash
Recover
Fire Blast
Sunny Day
Gust

There is one more Pokémon obtainable in this game, but unfortunately it was only available for a limited time within Japan and in the Virtual Console

#251 Celebi

Location: Ilex Forest

Method:
To acquire a GS Ball you have to connect the game to the mobile phone with the Pokemon Mobile Phone System GB. This cannot be done in the US. You must have all 16 badges, beat a minigame, and complete a quiz to have the attendent at the Pokemon Communication Center in Goldenrod City give you a GS Ball.
In the Virtual Console release, you will receive the GS Ball at the Goldenrod City Pokémon Center after you have defeated the Elite Four, without needing to go through Kanto.
Once you have the GS Ball, take it to Kurt to have him inspect it. After the turn to the next day he'll tell you about a strange presence in the ball before dashing outside. Follow him and he'll say Ilex Forest is uneasy and that you should check it out with the GS Ball.
The trees will be rustling in the forest. Take the GS Ball to the shrine. When asked if you want to put the GS Ball in the shrine, say yes and Celebi will arrive to challenge you. Celebi holds no special items. Grass/Psychic is weak to Fire-, Flying-, Ghost-, Dark-, Ice-, and Poison-types and has a double weakness to Bug-types but offers good STAB and learns powerful moves like Giga Drain, Psychic, and Solarbeam. Because you need all 16 badges to fight it but is faced at a low level of 30, it would be wise to bring something that can inflict status before it uses Safeguard but not OHKO it.

Celebi
Level 30
OT:Yours
ID:Yours
Hold Item:
None
Heal Bell
Safeguard
Ancientpower
Future Sight