Scyther is a solid option in the Pokemon Red & Blue metagame due to its strong attack and speed stats, and access to good moves like Sword Dance and Slash.
The name of the game for Scyther is Sword Dance setup, before Slash. The only thing that holds this Pokemon back is its meager bulk. Unfortunately, this does hold it back pretty hard, so far that it only really sees play in the UU category. Singles (more so Smogon) plays on tiers that go from OU (OverUsed), UU (UnderUsed) and so on. Here is the best moveset for Scyther in Red & Blue.
Note: This list is subjective and reflects only the opinion of the writer.
The best moveset for Scyther in Pokemon Red and Blue
Slash
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Slash is Scyther's best way of dealing damage. Slash is an amazing move in Red & Blue since it nearly always produces a critical hit, especially after an Agility (which is a good option for this moveset).
Most Pokemon that learn this move will use it, like Persian. Setting up a Swords Dance or Agility, then using Slash, can be extremely strong.
Swords Dance
Swords Dance is one of the best setup moves in the game. Swords Dance gives the user +2 in its attack stat, effectively doubling its attacking power. Due to Scyther's above average speed, this can be extremely effective if it can make use of a switching turn.
Swords Dance can be a solid option on lead if the opposing Pokemon opts to switch right off the bat. Be careful not to get paralyzed, as many lead Pokemon will use Thunder Wave early.
Hyper Beam
Hyper Beam offers the most raw damage to Scyther. Of course, if Slash strikes a critical hit, it will deal a huge amount of damage, but if something is low, Hyper Beam is a great choice.
Since Hyper Beam doesn't require a recharge turn if it brings about a knockout, this can be an extremely viable finishing blow.
Agility
Agility can be another extremely useful setup move. Agility raises the user's speed stat by two. This is especially useful for Pokemon with Slash, since critical hit likeliness plays off of the user's speed stat. After an Agility, Slash will almost always hit a crit.
This slot could be used for a different move, as the other three are completely necessary. This slot could become Toxic for Wall breaking, but Agility will likely be more useful more frequently.
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