Move mastery (Japanese: 技の皆伝move mastery) is the signature mechanic of Pokémon Legends: Arceus, allowing a Pokémon to use a move in the agile style (Japanese: 早業Swift Move) or strong style (Japanese: 力業Force Move). Using the agile style reduces a move's power and effects, but will either increase the user's action speed (for moves that affect the user) or decrease the target's action speed (for moves that affect an opponent), typically allowing the user to make their next move sooner. Using the strong style increases a move's power, effects, and accuracy (if not already 100%), but decreases the user's action speed, causing the user to move later in subsequent turns. Using either style also costs 2 PP; this works by deducting an additional PP from the move after it is selected, meaning that a move with 1 PP remaining can be used in either style.
If a Pokémon can learn a move by leveling up, then it can also master that move by leveling up. Zisu, at the Training Grounds, can also help a Pokémon master a move in exchange for a Seed of Mastery, including moves she serves as a Move Tutor for (which cannot be mastered any other way). In the wild, alpha Pokémon may come with one of these Move Tutor moves already in its moveset, in which case this move will already be mastered. Mastered moves are indicated by a icon on the summary and move selection screens.
The moves Teleport, Mimic, Splash, and Struggle can never be mastered. Rotom cannot master the special moves associated with its appliance forms.
Effects of mastered moves
Status moves and moves with secondary effects are also affected by the agile style and strong style in ways besides power and action speed.
Even though in-game text states that using agile style moves increases the user's action speed, only self-targeting moves actually do so. Agile style moves that target an opponent work by lowering the opponent's action speed. Therefore:
Knocking out an opposing Trainer's Pokémon with an agile style move will not affect the action order against the next Pokémon.
In battles against multiple Pokémon at once, using an agile style move against one target will not cause the user to move ahead of the other foes.