Thought Pokemon battles were already complex? Get ready for double the complications with Double Battles! (Actually, it's not really that more complex... Please don't run away now!)
First appearing in Ruby and Sapphire a decade ago, Double Battles are just as you'd expect: two Pokemon versus two Pokemon in the same battlefield.
There are two types of Double Battles--normal ones between you and a single opponent or group Double Battles that can be between 4 trainers, two on each side, or perhaps 2 versus 1 (or the other way round). Either way, the mechanics are the same; the difference is who controls what Pokemon.
In Double Battles, the first two Pokemon in your party are sent out simultaneously. Each turn, you pick one move for each Pokemon and your opponent does the same. Because you're facing against two Pokemon, you can often select a Pokemon to target, although some moves offer no choice.
Some moves such as Dazzling Gleam deal damage to both of your opponent's Pokemon--look for the keyword "damages opposing Pokemon". Other moves such as Earthquake target all Pokemon--friend and foe.
Battles play out similarly to Single Battles, with the Pokemon with highest Speed moving ahead of the others. At the end of each turn, if one or more Pokemon on either side has fainted, the trainer must send out enough Pokemon to fill the spaces (or their last remaining Pokemon).
Intricacies of Double Battles
So far, easy to follow, right? On paper, Double Battles shouldn't sound much more complicated than normal. You've just got one extra Pokemon on your side and one extra Pokemon on the opponent's side. No biggie!
This is where you're wrong though--especially against human trainers, less so against computer-controlled trainers. There's a reason why Double Battles is the chosen battle format in the official Pokemon VGC (Video Game Championship) held each year and that's because of all the extra complications.
First off, the options available to you in Double Battles have increased immensely. Even just looking at the Pokemon in battle, ignoring all other factors for a moment, do you focus both of your Pokemon's attacks on one of your opponent's Pokemon or try to spread out the damage evenly?
Well, if you focus everything, you could potentially KO one of your opponent's Pokemon, leaving them with a distinct disadvantage. But what if your opponent predicts this and uses Protect on the Pokemon you're planning to target or they switch out that Pokemon with a Pokemon that resists your moves?
That's... not good. Meanwhile your opponent's other Pokemon can attack your Pokemon completely unhindered or perhaps uses a status move or stat-boosting move to shift the momentum towards their favour. Which is doubly not good...
However, perhaps you already anticipated this possibility and instead focus your attacks on the other Pokemon. Your opponent would waste a turn using Protect or switching out and their other Pokemon, which they thought you weren't going to attack, gets blasted to oblivion.
Basically, there are a lot of mind games involved, moreso than in Single Battles, which can easily devolve into a frenzy of Pokemon switching. Well, so long as Stealth Rock and Spikes are nowhere to be seen. Because of this factor, a lot more Pokemon are viable in Double Battles.