I've started building my competitive team a while ago. As of right now, it consists of Blastoise, Chesnaught, Espeon, Talonflame, Dusknoir, Scizor, and Blissey. Blastoise is a wall of my team, and so is Chesnaught. Dusknoir used to be a wall too, but I decided to switch it up to a tank as it can take hits quite efficiently and hit back even harder. I've decided to make Talonflame is a special sweeper, because its Special Attack stat is pretty high. It's got a lot of special-based moves in its arsenal as well, which it can take full advantage of. I'm using Espeon as a dual screener. It has great Speed stat, which enables it to set up Reflect and Light Screen in an instant. Plus, this Pokémon's also got access to Magic Bounce, which allows it to redirect all non-damaging moves that opponents use (Roar, Taunt, and Stealth Rock would be some good examples). Blissey is used more as a supporting Pokémon, as it has access to moves like Wish, Aromatherapy, Heal Bell, etc. Scizor—I'm utilizing it as a physical sweeper. It has the Technician ability, which powers-up all of its moves that have sixty base power. Thanks to that, and with a little bit of help from Swords Dance, Scizor can wipe out your opponent's team entirely with Bullet Punch. (:
The biggest threat to my team would have to be fire-types. Scizor and Chesnaught are both quite weak to them. I may have to replace one of these Pokémon eventually, because fire-types are pretty common in competitive play, and being vulnerable to them—even a little—wouldn't be too much of a smart choice. If I do replace either of them, then I'll most likely go with Garchomp.
