ATTACK PRIORITY

In battle, the order in which each Pokemon takes their turn is determined by a few different factors. Generally, in singles battles, the fastest Pokemon will strike first and the slower Pokemon will move after it. Likewise, in double battles, the turn order for the four Pokemon is decided by the Speed stats of the individual Pokemon. This much should be fairly obvious. But how come moves such as Quick Attack won't always go first, as claimed?

The answer is this: every move in Pokemon is assigned a priority number. Moves with higher priority numbers will always go before moves with lower priority numbers, regardless of the Speed stats of either Pokemon. If two moves have the same priority number, however, the faster Pokemon will strike first per usual. Almost all of the attacks in the series have been given priority zero, but there a few moves of each priority number from Priority 5 down to Priority -7 (except for Priority -2 which includes no attacks as of Diamond and Pearl).

The priority levels, and the moves classified under each, are as follows:

It is also important to note that, under normal circumstances, switching out a Pokemon will outspeed any attack performed by the opponents (or teammates), regardless of their priority; thus, switching can be pseudo-classified as "Priority 6" and outranks almost everything. However, if the opponent of a switching Pokemon performs Pursuit, it will always strike the switching Pokemon before it can exit the field. Since this is merely a special case of the Pursuit attack, it's an exception rather than its own priority number. These priorities are not affected by Trick Room; during that particular move, higher priority moves still go first, but the slower Pokemon will go first if both Pokemon pick moves of the same priority.

Moves that "copy" or generate other attacks, such Assist, Me First, Metronome, Mirror Move, Nature Power and Sleep Talk, notably have Priority 0. If these attacks generate moves of different priority levels, they perform them immediately. This is only particularly useful for generating Roar and Whirlwind out of priority. (Also, if both Pokemon use Roar, the faster one still goes first and removes the opponent from the field.) Avalanche and Revenge cannot stop Focus Punch, but they will get their power boosted from it.

Some other, less commonly seen factors that determine move order are held items. Regardless of the Speed stats of any of the Pokemon on the field, a Pokemon holding Lagging Tail or Full Incense will always go last when the battle participants have selected moves of the same priority. It should be pointed out that Iron Ball merely lowers the holder's Speed rather than directly altering move order; an Iron Ball Pokemon will still go first if it's somehow faster than another Pokemon on the field. Quick Claw has a 20% chance of making a slower Pokemon strike first when both Pokemon have selected moves of the same priority; when Custap Berry activates, it works like a guaranteed Quick Claw for the Pokemon's next turn only. All of these held items ignore the effects of Trick Room.

Similarly, Sableye's unique ability, Stall, will make Sableye always go last when it and its opponent have selected moves from the same priority bracket. If two Stall Sableyes are battling each other, the "faster" Sableye will go last when they've picked moves of the same priority; also, if a Stall Sableye is facing a Pokemon holding Full Incense or Lagging Tail, the latter will move last. Like the held items, Stall Pokemon still go last during Trick Room.