As with many Pokémon who have appeared since the first generation, some of Scyther's Pokédex entries have been reused over the years. I've noted which ones below.
Red/Blue/LeafGreen: With ninja-like agility and speed, it can create the illusion that there is more than one.
Yellow: Leaps out of tall grass and slices prey with its scythes. The movement looks like that of a ninja.
Stadium: Moves incredibly quickly and shreds its enemy with its razor-sharp scythes. On rare occasions, it flies with its wings.
Gold/Stadium 2/HeartGold/Y: It slashes through grass with its sharp scythes, moving too fast for the human eye to track.
Silver/SoulSilver: When it moves, it leaves almost a blur. If it hides in grass, its protective colors make it invisible.
Crystal: It's very proud of its speed. It moves so fast that its opponent does not even know what knocked it down.
Ruby/Sapphire: Scyther is blindingly fast. Its blazing speed enhances the effectiveness of the twin scythes on its forearms. This Pokémon's scythes are so effective, they can slice through thick logs in one wicked stroke.
Emerald: Its blindingly fast speed adds to the sharpness of its twin forearm scythes. The scythes can slice through thick logs in one wicked stroke.
FireRed/X: It tears and shreds prey with its wickedly sharp scythes. It very rarely spreads its wings to fly.
Diamond/Pearl: It is nearly impossible to parry its attacking scythes. Its movements are like a ninja's.
Platinum/Black/White/B2/W2: The sharp scythes on its forearms become increasingly sharp by cutting through hard objects.
Uh, I don't know about you, but I'm not getting in a Scyther's way. Not if you paid me. Nope.
Most of these Pokédex entries are reflected in its learnset. Though Scyther has wings, it can't learn Fly — that's because it doesn't use them for flight, it uses them to be more agile. Naturally, it learns moves like Feint, Double Team, and Agility, reflecting how speedy and evasive it is.
I find it particularly interesting that its colors are for camouflage. Scyther's evolution isn't naturally occuring, requiring human interaction, and, well, Scizor, is bright red. It wouldn't last a minute in the wild. Scyther are designed to be deadly killers in the wild, and it benefits them to have their prey never realize they're coming. By evolving into Scizor, they lose everything that makes them so effective in the wild.
Also, given its origins, you might think they would have put a mention of sexual cannibalism in there somewhere, but it's nowhere to be found. Pokémon is a game for kids, after all.