I've noticed most experienced players seem to advise against the use of purely-Defense boosting moves, like Amnesia, Cosmic Power, Iron Defense, etc., and I just wanted to discuss their viability, especially in LU and RU. Firstly, most defensive boosters rely on Toxic to do damage (With a few exceptions, like Sigilyph), meaning Steel and Poison types wall them completely. That said, Steel Pokemon aren't nearly as common in NU and LU/RU, and Poison types aren't really a staple anywhere, notwithstanding things like Weezing and Drapion. After Steel and Poison types are removed, the other thing defensive boosters need to worry about are phasers (I find Cradily makes an excellent solution to this). Now, of course defensive boosters are inherently set-up bait for more offensive sweepers (Go to hell, Klinklang...), so a good defensive booster should ideally be paired with a sturdy revengekiller, in case things go wrong. Also, defensive boosters' own weapon can often be turned against them; Toxic will severely limit their lifespan. As such, Rapid Spin and Heal Bell support is always appreciated.So anyways, I'll wrap this rant up with a few defensive booster sets.
Shuckle @ Leftovers (NU/LU)
Bold - Contrary
252 Sp. Def, 176 Defence, 80 HP
Cradily @ Leftovers (NU/LU)
Bold - Suction Cups
252 HP, 200 Defense, 56 Sp. Def
Deoxys-D @ Leftovers (OU)
Calm - Pressure
252 HP, 132 Sp. Def, 128 Defense
Sigilyph @ Flame Orb
Timid - Magic Guard
252 Speed, 252 HP, 4 Sp. Atk
I'll edit this later and add descriptions, maybe meat the whole post up when I have the time, I just want to know everyone's thoughts on defensive boosters.