Steelix

Gold / HeartGold: Its body has been compressed deep under the ground. As a result, it is even harder than a diamond.

Silver / FireRed: It is said that if an ONIX lives for over 100 years, its composition changes to become diamond-like.

Crystal: The many small metal particles that cover this POKéMON's body reflect bright light well.

Ruby / Sapphire: STEELIX lives even further underground than ONIX. This POKéMON is known to dig towards the earth’s core. There are records of this POKéMON reaching a depth of over six-tenths of a mile underground.

Emerald: STEELIX live even further underground than ONIX. This POKéMON is known to dig toward the earth’s core, reaching a depth of over six-tenths of a mile underground.

LeafGreen: Its body has been compressed deep under the ground. As a result, it is even harder than diamond.

Diamond / X: Tempered underground under high pressure and heat, its body is harder than any metal.

Pearl / Y: It chews its way through boulders with its sturdy jaws. Its eyes can see in the darkness underground.

Platinum +3: It is thought its body transformed as a result of iron accumulating internally from swallowing soil.

SoulSilver: It’s said that if an ONIX lives for 100 years, its composition becomes diamondlike as it evolves into a STEELIX.

Black 2 / White 2: The iron it ingested with the soil it swallowed transformed its body and made it harder than diamonds.

Omega Ruby / Alpha Sapphire: Steelix lives even further underground than Onix. This Pokémon is known to dig toward the earth’s core. There are records of this Pokémon reaching a depth of over six-tenths of a mile underground.

Sword: It is said that if an Onix lives for over 100 years, its composition changes to become diamond-like.

Legends: Arceus: This Pokémon evolved through use of a strange item. Its body is coated with steel powder and notably hard—not even diamond can leave so much as a scratch.