Catch Entei in Pokémon Leaf Green

Entei, like the other Legendary beasts, is a very hard Pokémon to catch. But with time, and a lot of luck, you should soon have Entei.

Steps

First of all, you must have chosen Bulbasaur for your starter. If not, you can't catch Entei without cheating or hacking. You also must have beaten the Elite Four and have the National Pokédex.
Buy about 20 Max Repels. If you need more later, buy them.
Get a Pokémon at level 49 or very close to that level. You can get a level 49 Pokémon in Cerulean Cave.
Put the level 49 Pokémon in the lead slot. Put on a Max Repel.
Remember, Entei changes its area when you enter a new location, such as changing routes, entering caves, or entering a town. He moves even farther away when you Fly.
- Entei may move to the route you just entered, with a ton of luck! By the way, you need the Repel and level 49 Pokémon because Entei is level 50. It repels all other Pokémon.

Remember, Entei will not be found in caves.
If you didn't choose Bulbasaur, Squirtle will give you Raikou, and Charmander will get you Suicune.
If you get sick of searching, just put your game down and try again when you feel like it.
If he faints, turn off your game and don't save, because you will never see it again.
Use the Pokédex to keep track of its location.
Putting it to sleep will help.
If you haven't already, use your Master Ball on it, or it will run away. If you want to catch it without the Master Ball, use a move like Mean Look to keep it locked in place, or have a Pokémon with the Shadow Tag or Arena Trap ability in the front of your party.
Slowly whittle down its HP with False Swipe or moves that do little damage.