After FLCL's suggestions, your team looks very solid!
I just have one recommendation: Switch Substitute on Amoonguss for Clear Smog. Clear Smog can completely stop threatening sweepers trying to set up on you, and is in general much more effective than Substitute. I would say switch Sludge Bomb for HP Ice, but you say you already tried it and didn't find it so effective, so no problems there I suppose :)
Overall this is a very cool team! Is Imposter Ditto really NU? WOW! :p
I wouldn't get used to that haha, as I can see that moving up to OU really quickly...it's very helpful!