Your first team in Uranium

[Dragonstrike]

I don't know about how hard it is to counter him in competitive, but in single player, Nucleon is overpowered beyond belief. Especially once you get to Tsukinami village and gain access to the Choice Scarf...

But yeah, I probably would have had a much harder time of it if I hadn't read spoilers on the wiki before playing. As it stands, I was able to defeat Gamma Urayne in one turn with Nucleon + Focus Sash + Mirror Coat, but I suspect that fight would have been a nightmare if I didn't see it coming far in advance.

Nucleon is, quite literally, uncounterable.  It literally has an answer for everything and will decimate anything that even attempts to wall it.  There are gimmicks and very mediocre pokemon that can attempt to counter it, but they're so few in number and/or incredibly niche that it doesn't even matter in the long run, since you can pack several pokemon to counter those few potential 'counters' Nucleon has.  In short, it's just as ridiculously OP in multiplayer as it is in the single player...

Hmmm...well, that's one way to beat Gamma Urayne.  Simple, quick...but yeah, players are unlikely to have that kind of setup if they don't know that fight's coming.  If you think Nucleon is bad, well...Gamma Urayne is even more fun.  But at least Overheat and Proton Beam cripple what it can do with special attacks and make it much more manageable...and then it pulls out Atomic Punch...