Multiscale

Multiscale is an ability that reduces damage taken from attacks by 50% when the user is at full HP. This makes Pokémon with Multiscale much more durable at the start of battles, allowing them to potentially survive powerful hits that would otherwise knock them out.

You only see this ability on Dragonite and Lugia - both as hidden abilities. It is a very useful move because it allows these Pokémon to set up or fight back without fear of fainting immediately.