If you're gonna use it as a mixed attacker, I seriously suggest that you use 2 physical and 1 special attack. If you're not gonna use its 130 base attack at all, well, go for it but I seriously hope you know what you are doing. Its base special attack is a mere 80, in case you were wondering.
Just one point? If it's in speed, it can. If it's in HP, it can depending on whether or not it's a sub user. If it's in anything else, not really. You DO mean it's missing one point, not one IV, right? Because missing the IV can hurt.
That was a good battle too. You need a bit of work on predicting though. Mega Alakazam is too frail for my taste but maybe you can use it better than I can. Manectric is a good replacement IF you can find one with a good Hidden Power. Azumarill's Play Rough against Salamence was easy to predict, you should have gone for Rotom instead.
Most things carry Protect, so if you see an easy super-effective, there's a good bet that your opponent will Protect. It's not always true but it does happen fairly often, enough that you can use it to your advantage. Rotom and other 'mon that suffer from TOO MANY GOOD MOVES NOT ENOUGH MOVESLOTS or really good at absorbing hits sometimes doesn't carry Protect. If you're stuck guessing whether or not they're gonna use it, hit the one that is less likely to have it.
Lastly, turn 6, you should have gone after Garchomp because Amoongus walls Rotom-W. Seriously, what's Thunder or Hydro Pump gonna do to it? The HP drain might have let you survive Rotom's hit and let you have a chance to kill it.