Generation V
Weak Armor
Physical attacks lower Defense and raise Speed.
Detailed Effect
Whenever a physical move hits this Pokémon, its Speed rises one stage and its Defense falls one stage. This ability triggers on every hit of a multiple-hit move.
Pokémon With Weak Armor
25 canonical Pokémon forms can have this Ability.

Roggenrola
Boldore
Garbodor
Sinistea
Polteageist
Cursola
Galarian Corsola
Garbodor Gmax
Onix 
Omanyte 
Omastar
Kabuto
Kabutops
Slugma
Magcargo
Skarmory
Dwebble
Crustle
Vanillite
Vanillish
Vanilluxe
Vullaby
Mandibuzz
Armarouge
Ceruledge