If I equip a Passho Berry to Landorus and face Urshifu-RS, does the Passho Berry reduce the power of all three of Urshifu's Surging Strikes in one turn, or just the first of that turn's Surging Strikes?
I did a two test replays, one With the Passho Berry and one Without the Passho Berry. In the Passho Berry replay, the Passho Berry reduced the damage to 22% only for the first strike, as the damage the second strike of Surging Strikes did without the Passho Berry was 48-49% in the battles. This means that Passho Berry only reduces Surging Strikes' damage on the first turn, and not all 3 turns.
Hope this helps!