Can a Scyther with FC/BB be useful against mewtwo?
Sure as a typical glass cannon. He will do fine damage but due to resistances will perform worse than a Scizor who has resistances. Against confusion he will take a special beating comparatively.
If you aren't spending dust he's like all other glass cannons that will die at or around the special depending on the quick move.
He isn't surviving focus blast he will barely get there if it has confusion.
In sims at level 34.5 he doesn't even make it to FB without dying if it has confusion. So he does his glass cannon stuff but his resistance to FB is kind of a moot point like many "FB counters" for Mewtwo. The truth is if mewtwo has C/FB your whole raid group needs to be on their game and just be ready to throw bodies at this thing.
You've got a legacy pokemon there. Bug Buzz is no longer available for Scyther. I wouldn't do much to it when it comes to raids or certainly don't evolve it. I'd hold on to it because people that love Scyther like me might give you its weight in gold if and when trading comes out. I'd look elsewhere for your mewtwo counters because of the possible value of that mon.
Wow, that's insane! I'm jealous! I wouldn't. There are more Scythers to be found, but none like yours. You have to ask yourself if you like rarity over functionality. With STAB being lowered, it makes it easier to hold onto mons like that I think. It may never be useful but what makes you feel good when you look at your pokemon? That's really the only question that matters.
Average DPS is comparable to Scizor, he just is a little frailer. But just remember that glass cannons typically do less DPS than Supreme counters. So as an addition to your TTars he'll probably do fine but he shouldn't replace a Ttar.
I saw that first hand today when going up against a Zam (as mewtwo practice). Tried a lineup of Gengar, Scizor, B/C Ttar, B/C Ttar, other assorted high DPS choices scizor, gengar, SE Ttar etc. and kept timing out. Then I switched to Gengar, B/C Ttar, B/C Ttar, B/Se ttar and won. I shouldn't have tried being cute.
