Butterfree learns Confusion as it's first move. Lv. 10.
If you for some reason do not have the movie in a Butterfree of higher lv. simply either breed a new Caterpie or visit the move re-learner in his house on Island Two for him to teach it the move again (costs either 1 Big Mushroom or 2 TinyMushrooms).
Dragonair does not learn Dragon Rush in Pokemon Leafgreen. However, it can learn the move in Pokemon Diamond, Pearl and Platinum at level 39.
It can't learn fly
Cut,Strength,Rocksmash.
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It's not possible to learn Draco Meteor in Leafgreen due to it not existing until Generation 4 games like Diamond.
No, Butterfree cannot learn Fly.
Butterfree learns confusion at level 12.
YES!
If your Pokemon evolves later it could learn more attacks in its pre-evolved form that maybe could not learn if evolved (particularly true with Pokemon who evolve from stones) or it could skip some attacks that should learn in its evolved form. In this case, it is not important, because butterfree will learn Confusion at level 12.
The moves that Butterfree will learn in Pokémon LeafGreen are Confusion, Sleep Powder, Poisonpowder, Stun Spore, Supersonic, Whirlwind, Gust, Psybeam, Silver Wind, Safeguard, TM moves of Toxic, Hidden Power, Sunny Day, Hyper Beam, Protect, Rain Dance, Giga Drain, Frustration, Return, Solarbeam, Psychic, Shadow Ball, Double Team, Aerial Ace, Façade, Rest, Secret Power, Attract, Thief, Skill Swap and the HM05 move of Flash.
A typlosion can learn explsion
The first Psychic Pokemon you can gain in FireRed is Abra, North of Cerulean, but you can use Butterfree as well which can learn Confusion, Psychic among other moves (Caterpie/Metapod north of Viridian)
Dragonair does not learn Dragon Rush in Pokemon Leafgreen. However, it can learn the move in Pokemon Diamond, Pearl and Platinum at level 39.
learn how to spell.
All Pokemon with a water-type can learn it. There are some other Pokemon that can learn it, but mostly water-Pokemon.
In Red and Blue, it learns Confusion at Level 12, two Levels after it evolves from Metapod. In every other game, it learns Confusion at Level 10, as soon as it evolves from Metapod.
Butterfree is better but if you train oddish it will evolve to gloom then use a sun stone or leaf stone to evolve it to vileplume/bellossom which are a little better than butterfree but butterfree can learn psychic type moves which can defeat vileplume and bellossom so choose butterfree if you want that but if you want an offensive and defensive Pokemon choose vileplume.