Use Power Split if you want a move to give shuckle attack. With its horrid attacking stats, any other pokemon would give you a boost. And if they are using an offensive pokemon, then you just crippled it.
I want a pet Lavos Spawn. [Order of the Cetaceans: Phocoena dioptrica]
Gyro Ball is still affected by your Attack stat and STAB, just the base power depends on the difference between yours and your opponent's speed. So using a Contrary Shell Smash wouldn't impact the damage much, if at all. Use Agility or another Speed-buff move instead.
Playing) Fire Emblem: Awakening, Guild Wars 2 Waiting) Pokemon XY