Koknodon

Diamond: It lived in jungles around 100 million years ago. Its skull is as hard as iron.

Pearl: It was resurrected from an iron ball-like fossil. It downs prey with its head butts.

Platinum +4: A lifelong jungle dweller from 100 million years ago, it would snap obstructing trees with head butts.

HeartGold / SoulSilver: CRANIDOS toughen up their already rock-hard heads by headbutting one another.

X / Omega Ruby: It was resurrected from an iron ball-like fossil. It downs prey with its headbutts.

Y / Alpha Sapphire: A lifelong jungle dweller from 100 million years ago, it would snap obstructing trees with headbutts.

Sun: It lived in jungles around a hundred million years ago. It used its skillful headbutts to combat Aerodactyl.

Moon: In rock layers where Cranidos fossils are found, the fossilized trunks of trees snapped in two are also often found.

Ultra Sun: A primeval Pokémon, it possesses a hard and sturdy skull, lacking any intelligence within.

Ultra Moon: Its hard skull is its distinguishing feature. It snapped trees by headbutting them, and then it fed on their ripe berries.

Legends: Arceus: An incredibly rare sight. They duel each other by ramming their heads together, and the resulting sound echoes throughout the area like the pealing of a bell.