Gen 9 update and guess what......GALLADE GOT SHARPNESS WHICH IS INNSSSAAANEEE due to all of the slicing moves it learns which include leaf blade,psycho cut,night slash,slash,sacred sword,and the new aqua cutter.
So here is the set
Evs:252 Atk, 252 Sp, 4 Hp
Leaf Blade/Night Slash/Aqua Cutter
Ok so personally I would get leaf blade or aqua cutter over night slash (usually leaf blade) but it's ur choice of coverage.
Sacred Sword and Psycho Cut are stab moves and hit VERY hard especially if you tera into same type.
Agility doubles you speed so you can clean up weakened teams or possibly sweep early game..
You should probably pair it with orthworm or cyclizar with shed tail depending on the format your in so you can be protected from physical moves while you set up.