Haspiror

Diamond: It slams foes by sharply uncoiling its rolled ears. It stings enough to make a grown-up cry in pain.

Pearl +2: When it senses danger, it perks up its ears. On cold nights, it sleeps with its head tucked into its fur.

Platinum +4: Its ears are always rolled up. They can be forcefully extended to shatter even a large boulder.

HeartGold / SoulSilver: You can tell how it feels by the way it rolls its ears. When it’s scared, both ears are rolled up.

Black 2 / White 2: By extending its rolled-up ears and striking the ground, it can bound so high it surprises itself.

Ultra Sun: Its arms and legs are weak, but when it rolls its ears up tight and then unleashes them with its full force, it can smash boulders to dust.

Ultra Moon: The reason it keeps one ear rolled up is so it can launch a swift counterattack if it’s attacked by an enemy.

Sword: If both of Buneary’s ears are rolled up, something is wrong with its body or mind. It’s a sure sign the Pokémon is in need of care.

Shield: Buneary can attack by rolling up their ears and then striking with the force created by unrolling them. This attack becomes stronger with training.

Legends: Arceus: My hypothesis as to why Buneary rolls up its ears is that its hearing is far too keen. I surmise that the Pokémon protects its hearing by limiting the sound that may enter its ears.