In Pokémon games, when the lead Pokémon of your party has the Synchronize ability there is a 50% chance that any randomly-encountered Pokémon will have the same nature as the Pokémon with the Synchronize ability.
How does this interact with SOS Battles in Sun & Moon? Will summoned Pokémon follow the same rules as random encounters, do they not interact with Synchronize at all, or will they always be influenced by Synchronize?
Best Answer
From this Reddit thread, it looks like Synchronize will work for SOS Pokemon, but it will only take the nature of the first Pokémon in your party into account:
This information is also supported here:
It appears that this was confirmed during the datamine of the Sun/Moon demo, the results of which were discussed here. The specific post that involves Synchronize is this one:
Basically, if you have a fainted Pokémon in the first position of your party, but your Pokémon with Synchronize is on the field, Synchronize will be giving SOS Pokémon a 50% chance to have the same nature as the fainted Pokémon, rather than the Pokémon with Synchronize.