Generation Vii
Shields Down
When its HP becomes half or less, the Pokémon’s shell breaks and it becomes aggressive.
Detailed Effect
When this Pokémon enters battle and at the end of each turn, if its HP is 50% or above, it changes into Meteor Form; otherwise, it changes into Core Form. In Meteor Form, it cannot be given a major status ailment (though existing ones are not cured), cannot become drowsy from Yawn, and cannot use Rest (which will simply fail). This ability cannot be copied, replaced, or nullified. This ability only takes effect for Minior.
Pokémon With Shields Down
14 canonical Pokémon forms can have this Ability.
Regular Ability 14 Pokémon
#0774 
Minior Red Meteor 
#10130 
Minior Orange Meteor #10131 
Minior Yellow Meteor #10132 
Minior Green Meteor #10133 
Minior Blue Meteor #10134 
Minior Indigo Meteor #10135 
Minior Violet Meteor #10136 
Minior Red #10137 
Minior Orange #10138 
Minior Yellow #10139 
Minior Green #10140 
Minior Blue #10141 
Minior Indigo #10142 
Minior Violet
Minior Red Meteor #10130 Minior Orange Meteor #10131 Minior Yellow Meteor #10132 Minior Green Meteor #10133 Minior Blue Meteor #10134 Minior Indigo Meteor #10135 Minior Violet Meteor #10136 Minior Red #10137 Minior Orange #10138 Minior Yellow #10139 Minior Green #10140 Minior Blue #10141 Minior Indigo #10142 Minior Violet