There are probably more differences from vanilla mechanics that I haven’t realized. Please tell me if you find one.
Stat Visualization
Items or abilities that modify the stats of a Pokémon affect the numbers shown on the Pokémon summary so they are not invisible to players.
Calculating Stats
When in battle, all calculated stats are affected by all callbacks to their calculations. This means that moves like Body Press, for example, will be affected by both Eviolite and Slow Start instead of having weird per-move exceptions.
EVs
- No EV rising mechanic has a max EV it can rise. 255 max EVs and 510 max EVs totals still apply, but vitamins, for example, are not limited to max 100 EVs.
- Pokérus always doubles EV increases, even from items.
Learning Moves
YAPU’s Pokémon’s learnsets may be wider than those of the official games since it has all moves. Learnsets are usually a combination of the SwSh, BDSP and SV learnsets.
Breeding and moves
Babies will know all egg moves learnt by the parents (not only their current moveset) and all level moves known by both parents (not only their current moveset). You may need to go to the move reminder to find the exact move you want but they will know it.
Freeze
- Frozen Pokémon thaw out on sunny weather.
- Frozen Pokémon thaw out when hit by fire moves.
Price Money
In vanilla Pokémon, money won on a battle is a base for the trainer type multiplied by the level of their last Pokémon. In YAPU, it is instead multiplied by the highest level among their Pokémon.
Eviolite
If a Pokémon that can’t evolve (like Ditto or Mew) is holding an Eviolite and transforms into a Pokémon that can evolve, eviolite will affect it, unlike in vanilla Pokémon.
Grounded Flyers
When a grounded Flying Pokémon (for example holding an Iron Ball) gets hit by a Ground move, the Ground-Flying effectiveness will be counted as 1x and then multiplied by the effectiveness of Ground against the other type of the Pokémon. In Vanilla Pokémon the final multiplier is always 1x regardless of the other type.
Megaevolution
Megaevolutions are performed at the start of the turn, even before switching.