When playing normally, players don't need much consideration what Pokemon they'll need to include to their team. Their favorite team can comprise of their favorite Pokemon with different types and movesets. You can beat your rivals, other trainers, the Elite Four and the Champions using higher-leveled Pokemon and simply exploiting enemy Pokemon weaknesses. It also helps that walkthroughs like this will give the player vital information beforehand like the trainer's Pokemon lineup, their level and other important notes to watch out for. The game also tells you what Pokemon your opponent will use.
Take note that the teams presented in this article are only a few of the many combinations. There's no such thing as a "perfect" team. For competitive battles, your luck has a considerable part to play with. Feel free to use your own tried and tested team. This is meant to provide ideas to the players that are just starting with competitive battles.
This page aims to give you as much tips and information about competitive battling, primarily focused on setting up your team and what important pointers to consider when building it.
Expect that your opponents will use carefully bred and trained Pokemon. There some who train and breed their Pokemon tediously just for the sake of creating a powerful Pokemon that can be used in battles. With that in mind, it doesn't matter if you're using a high-leveled team. In competitive battles, you and your opponent's Pokemon will have a fixed level for a fair fight. This is where Nature, EVs, IVs, abilities etc shine and hold advantage.
This should go without saying. Memorize the whole type-matchup chart. Knowing your Pokemon's strength and weaknesses will help you bring out the best in them. This is also imperative in exploiting your opponents' weaknesses and avoid using attacks that they're strong against. In this game, super-effective and non-effective moves can mean a matter of victory of defeat.
STAB stands for Same Type Attack Bonus which is applied to an offensive move that has the same type as the Pokemon using it. For example, a Gyarados (water/flying) using Surf will get a 50% damage boost compared to a Tyranitar (Rock/Ground) using the same move. Dual-type Pokemon can enjoy STAB damage on moves that are similar to any of their types at the risk of having the weaknesses of both types.
STAB damage can be further improved by equipping a Pokemon with a corresponding item. Items like Plates and Orbs for example boosts certain move types. Combine it with STAB and you'll be able to inflict more damage.
The game offers a large variety of items that Pokemon can hold. These range from items that boost damage from particular types, consumables such as herbs and berries, items that enable specific Pokemon to evolve when traded or even Mega Stones that enable specific Pokemon to change to their Mega Evolutions. You'll get these items across the Kalos region but some of the most useful ones are found in the Battle Maison as prizes in exchange for Battle Points.
The most popular choices are Leftovers, Expert Belt, Choice Band, Choice Specs, Choice Scarf and Focus Sash to name a few.
EV or Effort Values are points that boosts a Pokemon's stat. For every 4 EV points, one point is added to the actual stat. EV points are earned by defeating Pokemon in battle. A Pokemon can only earn 510 EV points to be considered as "Fully Trained" and you can only allot 255 EVs in one stat. This will allow you to max out two stats at once.
These extra stat points will matter in competitive battles. Assume every trainer you'll face will have a party of fully EV trained Pokemon. EV-trained Pokemon have the edge in competitive battles. Factor in careful IV breeding, Nature and good moveset selections and you can have the advantage in battle. EVs can get a bit technical so you can refer for more details in this dedicated page.
Each battle mode may require different Pokemon lineup if you're playing competitively. The Pokemon you set up as a support for double or triple battles may not do well when pitted alone in single battles. The same goes when using Pokemon who excel in single battles to group battles. The game offers several ways for you to get used of these different battle modes. There are some NPC trainers who will engage you in double and triple battles.
You'll be surprised to discover that the powerful team you used for crushing the game's NPCs and champions won't do well against good human opponents. Before going competitive, you may want to test your team in Lumiose City's Battle Institue or Kiloude City's Battle Maison. These places are good training grounds for newbies who want to form their PvP team.
You can also check out Battle Dining Restaurants in Lumiose City.
The game has over 700+ Pokemon, each with their own strengths and weaknesses. There are a lot of different combinations out there but building your all-star team will take time in research as well as trial and error. Sites like PokemonDB, Bulbapedia and Serebii provide much needed information about individual Pokemon stats, abilities, moves and many more that will help you plan ahead what movesets you'll like to teach your Pokemon. Smogon University is a perfect place to check if you're really serious about entering the competitive battling scene. They have very helpful articles dedicated to competitive battles and links to simulators too.
Are you a veteran of competitive previous gen Pokemon battles? Are you a new trainer, with this gen as your first Pokemon game? Or are you have you played older Pokemon titles, skipped a few versions before returning to the series again? Nevertheless, new mechanics, updated moves, abilities and effects are applied in this version of the game. It's worth knowing!
Now you've memorized the Type Matchup Chart, familiarized yourself with the new mechanics and move updates, practiced through different battle modes and finished the game. The next step is to know what type of team fits your style. An effective team consists of carefully trained, individual Pokemon which take advantage of each other's moves and abilities. Are you an aggressive attacker? Then you can building a team of heavy hitters which will deliver relentless damage to your opponents. Are you a technical trainer who prefers to manipulate the tide of battle through status effects and buffs/debuffs? Then include defensive Pokemon to stall your opponents and support Pokemon to provide the non-offensive yet manipulative moves.
The diversity and variety of Pokemon is large since you can only choose up to six out of the 700+. That said, some Pokemon excel at certain "roles" fit for their movesets, innate abilities, stats and growth patterns. Here are some of the roles you can consider when building your team: