I have noticed an issue on Showdown involving abilities such as: Dazzling, Queenly Majesty and Armor Tail in regards to Double Battles.
I will attempt to describe this as clear as possible.
On Turn One, you lead Grafaiai who's ability is Prankster and Urshifu- Single Strike.
Your opponent leads Ampharos and Farigiraf with the ability Armor Tail.
On turn one, everyone besides Urshifu clicks Protect, and Urshifu clicks Wicked Blow on Ampharos.
On Turn Two, Grafaiai uses Encore on your own Urshifu, and your Urshifu clicked Sucker Punch, targeting the Farigiraf. Since Priority is determined at the time of move selection, Urshifu and Grafaiai will both have +1 Priority on their moves. Grafaiai is faster than Urshifu, causing Encore to go first and then force Urshifu to use Wicked Blow instead. Here is where the difference occurs:
On Cartridge, Farigiraf's Armor Tail ability will block the Wicked Blow due to it now being a Priority Move.
On Showdown, the Wicked Blow will still go off and hit the targeted Farigiraf.
I don't know if this is an actual bug or just a niche interaction that was never tested, but none-the-less I would like to spread this information around.
Here is a link to a game a friend and I set up to show off the described:
https://replay.pokemonshowdown.com/...-2000647732-gez7yl68j88quh3f4okzcwcmw9b5l0vpw