How did this Pokémon go first?

Question

https://replay.pokemonshowdown.com/gen8nationaldexag-1373902072

I had Timid, Max Spd Evs on Caly-S. How did Greninja go first?

Answer 1

Water Shuriken is a priority move.

Water Shuriken attacks with increased priority.

Source

Comments

I actually never knew that lol.