Pokémon SAlt Crystal

Everything that changed in battle.

Levels, Stats and Experience

All Pokémon play with lv. 50 stats, at all times, regardless of the level you see on display.
DVs and Stat Experience were removed from stat calculation. Instead, a slightly less impactful bonus to stats is granted via level up (+1 to all stats every 4 levels).
Badge stat boosts were removed from the game.
Stat levels have mechanics heavily based on Pokémon Legends: Arceus. They range from -1 to +1 and have a duration in turns, after which they expire. In addition, status moves that boost or hinder stats affect both offensive and defensive stats.
The amount of experience points granted after battle has been doubled.
Traded Pokémon no longer received boosted experience.
Obedience rules apply equally to all Pokémon, traded or otherwise.
Boosted the obedience level cap when the player has no badges to level 25.

Power Points

PP is now a single pool of energy for all moves.
The maximum amount of PP varies per species and is calculated based on the species' Base Stats (Base Stat Total divided by 12).
PP is fully restored at the end of a battle.
While in battle, PP can be restored with items such as Elixer (on use) or Leppa Berry (held).
Certain moves (e.g. Spite) and status conditions (e.g. Sleep) affect PP restoration.
When selecting a move for which there is not enough PP, Struggle is used instead.

Moves and Effects

Known bugs from the original Crystal version have been fixed.
Mechanics mostly on par with generation 8 (SwSh, BDSP, PLA): Physical/Special split; updated Power and Accuracy of various moves; etc..
Irrelevant moves, or moves that were deprecated in generation 8, were replaced with more useful moves, to promote diversity.
Poison - In addition to dealing damage, it burns a tiny amount of PP (1 PP) every turn.
Sleep - Lasts between 2 and 3 turns. Taking damage wakes the sleeping Pokémon sooner. Restores some PP (4 PP) every turn spent sleeping (select Fight from the menu).
Freeze - Lasts between 2 and 3 turns. Taking damage thaws the frozen Pokémon sooner. Grants a boost to the defenses of the frozen Pokémon (similar to Reflect and Light Screen, stacks with these effects). Ends under harsh sunlight.
Flinching - Can carry over to the next turn, meaning that Pokémon going second can also flinch the opponent.
Rampage - Caused by moves such as Outrage. Locks the user into the move for 2 to 3 turns. Subsequent turns increase the move's Power (+20), but also make the user take more damage (+20 Power for the opponent).
Rollout and Fury Cutter are now regular Rampage moves (2 PP, 40 Power).
Multi-hit moves now always hit 3 times.
Triple Kick is now a regular Multi-hit move.
Critical Hit probabilities match generation 8 tables.
Belly Drum (2 PP) - Sharply raises Attack and Special Attack.
Spite (2 PP) - Burns 3 PP from the opponent.
Endure (2 PP) (Priority Move) - Direct damage taken is reduced by half until the user's next turn. When taking damage, the user consumes an additional 4 PP to survive with at least 1 HP and raise its Attack, Special Attack and Speed for 3 turns. This additional effect fails if there is not enough PP left.
Protect and Endure fail if the user is trapped with binding moves (e.g. Fire Spin or Whirlpool).
Mist (2 PP) - Protects the user against stat changes for 5 turns. Raises evasiveness for 3 turns.
Safeguard (3 PP) - Protects the user's party from status conditions for 5 turns. Raises the user's Defense and Special Defense for 3 turns.
Focus Energy (3 PP) - Raises critical hit ratio by two stages and makes the user recover 1 PP at the end of the turn, while active. Lasts 5 turns.
Hidden Power (3 PP, 50 Power) - Always hits for super-effective damage (Pokémon Legens: Arceus mechanics).
Growth (3 PP) - Raises the user's Attack and Special Attack. Under harsh sunlight, it also raises Speed.