Pokémon Gold and Silver/The Three Legendary Beasts
The three Legendary Beasts are Suicune, Raikou and Entei, and the former's moves depend on the versions. In Gold and Silver, Suicune has Leer, Water Gun, Roar, and Gust, and in Crystal it has Leer, Bubblebeam, Rain Dance, and Gust. This is likely because you can catch Suicune in Tin Tower in Crystal and the developers didn't want it using Roar. Entei knows Leer, Ember, Roar, and Fire Spin and Raikou knows Leer, Roar, Thundershock, and Quick attack. You get 1,234 EXP for defeating any of the Legendary Beasts.
All are Level 40.
 The Legendary Beasts
To find them first you need to see them, then you can find which area they are in. A good place to check is Route 36, because of its links to other routes. If the Pokémon is to the left of Ecruteak City, then go into the link place between Ecruteak and Route 38. It is also good to check the Pokédex, because if the Pokémon is on Route 39, you've got it.
The easiest way to catch one is to make the Pokémon fall asleep, then swap to a Pokémon that can lower its health. Mean Look and others are good, but they can still use Roar to escape.
To catch a Legendary Beast, a few steps are needed:
- You must have three different types of Pokémon in your party.
- Your Pokémon must have Flash, Sleep Powder, False Swipe (or Tackle if you don't have Scyther), 20-30 Ultra Balls, and two Fast Balls.
Flash is used to reduce the accuracy of the enemy's attacks. It is also used to light up dark areas, like in Dark Cave. You can get this skill from the Head Monk at Sprout Tower in Violet City. Sleep Powder is used to make wild Pokémon sleep. You can get this skill by catching Tangela or Weepinbell, as both Pokémon have it. You can locate these Pokémon on Route 44.
Scyther is a good Pokémon to use, because its False Swipe attack will take down enemy's health to 1HP, then miss every attack thereafter. You can find a Scyther in National Park. You can also use a low level Pokémon and the normal Tackle skill. Use level 20 to 25 Pokémon, because their Tackle skill will bring down the enemy's health from 1HP to 10HP per attack. You don't know how much HP the Legendary Beast has, so just get its HP down into the red. If you can leave just a little red on its health bar, it will be much easier to catch it.
You need few Ultra Balls as well. It's hard to find these balls, but you can buy them in Blackthorn City. You can get to Blackthorn City by following the Ice Path. At Blackthorn City, buy 20 to 30 balls before trying to catch a Legendary Beast. You also must have at least two Fast Balls. You cannot buy these balls; you can only find them or create them. The White Apricorn is an item used to create one Fast Ball.
Before you go into battle, make sure you line up your Pokémon party. The first Pokémon should know the Flash skill, like Magnemite or its second evolved form, Magneton. Use either Weepinbell or Tangela for your second Pokémon, either Scyther or any low level Pokémon with Tackle. Save your data at Tin Tower on your way to the fight.
During the fight, use Flash first to reduce the Legendary Beast's accuracy. Do this up to five turns until it says its accuracy won't drop any further. Then switch to your second Pokémon and put it to sleep. At this point, your goal is get the Beast's HP down into the red with your third Pokémon. If you get its HP down this low and it's asleep, it will be much easier to capture. Try the Ultra Balls for up to five turns, and then a Fast Ball, if they aren't successful. Keep alternating between five Ultra Balls and a Fast Ball until you catch the Legendary Beast.