Priority

Priority is a property of several moves and deals with the order of moves used in a turn. The most common type of priority-based moves are ones with increased priority. These moves will force the user to go first. Moves that give increased priority are generally damage dealing attacks that include Quick Attack and Extremespeed. Some moves are always given priority and are typically effect based moves that last the duration of the turn, such as Protect or Magic Coat. There are also moves that always give priority because they are generally responses to the other Pokémon's moves, like Counter and Metal Burst. At each tier, all ties are settled by the Pokémon's Speed stat.

For example, take the hypothetical battle between a Snorlax and Flareon facing a Charizard and Deoxys. Their respective Speeds are 100, 200, 300 and 400. Snorlax uses Protect, Flareon uses Quick Attack, Charizard uses Counter and Deoxys uses Extremespeed. Despite having the lowest Speed, Snorlax goes first with Protect because the move is always given priority. Although Flareon used Quick Attack, an increased priority move, Deoxys used Extremespeed, another increased priority move, and goes next because its Speed is higher than Flareon's. The last to move is Charizad. While its Speed is higher than Flareon's, it used a decreased priority move, Counter, and as such will always go last.