How to Snag the Legendary Pokémon of Blue, Red, and Yellow
Live the legend again!
With the re-release of the first-gen Pokémon games, you'll get a chance to catch the legendary birds and Mewtwo all over again. However, in the first-gen games, there's not a big to-do over the legendary Pokémon. They're not integral to the plot, and they're in places you don't really have to go.
This guide will tell you where to find the legendaries, their stats, and how to beat them best. But first, you'll need to gather some supplies and get ready for a few tough fights.
Suggested Equipment
Before you rush out to catch the legendaries, you should stock up on as many Ultra Balls as possible. Almost without fail, the legendaries will burst out of anything less than an Ultra Ball, even at 1 HP. Also, pay attention to type-matching. Each of the legendary birds is easily countered if you bring the right Pokémon. Mewtwo is a bit harder to counter since Psychic has no weaknesses in Generation One.The Legendary Birds
Articuno
No. 144
Freeze Pokémon
Pokédex: A legendary bird Pokémon that is said to appear to doomed people who are lost in icy mountains.
Articuno is an Ice-type Pokémon, one of the few that are actually in the first generation games. You can find it in the Seafoam Islands, but you'll need Strength and Surf to get it. It's best to bring a lower lever fire Pokémon like Charizard or Arcanine, and slowly chip away at it's HP with weaker Fire-type moves.
Zapdos
No. 145 Electric Pokémon

Pokédex: A legendary bird Pokémon that is said to appear from clouds while dropping enormous lightning bolts.
This Pokémon is an electric powerhouse, and it fittingly makes its next at the Power Plant. You'll only need Surf to make it to Zapdos. Rock and Ground-type Pokémon are Zapdos' bane, and if you bring along Onyx, Golem, or Rhydon when you go to face it, you'll have no issues.
Moltres
No. 146 Flame Pokémon

Pokédex: Known as the legendary bird of fire. Every flap of its wings creates a dazzling flash of flames.
This Pokémon is hidden at Victory Road, but it'll only take Strength to get there. You're best friend when trying to catch Moltres will be either a Water or Ice-type Pokémon. If you've already caught Articuno, it's a great Pokémon to use against Moltres.
Mewtwo
No. 150 Genetic Pokémon

Pokédex: It was created by a scientist after years of horrific gene splicing and DNA engineering experiments.
Mewtwo becomes available in the Unknown Dungeon near Cerulean City, and you'll need to get Surf and Strength to get to it. There's no type of Pokémon that's super-effective against Psychic-types in first-gen Pokémon so you'll just have to wear Mewtwo down the old fashion way. Just don't bring any fighting or Poison-type Pokémon or the fight won't go your way.