Fire Red's/Leaf Green's habitat pokédex page
Scyther coexists in the Grasslands with pokémon like Nidoking, Nidoqueen and Kangaskhan (all who live alongside it in the saffari zone too).
Nidoking is usually protrayed as very very territorial, though the pokédex doesn't elaborate on this behaviour. (And since my position stems primarily from the games, I will try to add specific proof from said games) What the pokédex does elaborate on is this:
"A Nidoking's thick tail packs enormously destructive power capable of toppling a metal transmission tower. Once it goes on a rampage, there is no stopping it." - Emerald
So assuming a Scyther angered a Nidoking enough to cause it to rampage, the Nidoking would've stop at nothing save most likely defeat.
Nidoqueen has a similar case to Kangaskhan (who we will see shortly), in that the pokédex states this:
"It uses its scaly rugged body to seal the entrance of its nest and protect its young from predators." - Silver
"It is adept at sending foes flying with harsh tackles using its tough, scaly body. This Pokémon is at its strongest when it is defending its young." - Emerald
If a Scyther decided to prey on a couple baby Nidoran, it would have to get past, literally, over the mother first. The moment which she is at her strongest.
Now onto Kangaskhan, who really I shouldn't even have to explain what they would do to a Scyther that tries to prey on their baby.
It should be noted, tho. Based on Scyther's description as "a ninja" on his various pokédex entries, that he more than likely uses stealth and ambush tactics against his prey. Since it is so fast, it shouldn't have a problem blitzing this three in order to prey on the young.
The problem here is precisely that. I don't think they would got into a confrontation against the two Nidos nor Kangaskhan. At least not directly. They would most likely stalk, keeping their distance. And when the moment is right, blitz into the respective nests for a quick kill and go away with the young before they even realize.
This is the more concrete proof I could find specifically using the games. Would it warrant a possibly? I honestly cannot say for certain. Would this upgrade their speed to contend with third stages (or at least prey on their nests)? That I would say it's certainly a "possibly".
