Steelix

Steelix is a / Pokémon and is the evolved form of Onix, Steelix can be obtained by making an Onix hold the Metal Coat and trading it. A well trained Steelix can be harder than diamonds.

Trivia

 * Steelix is the second largest Pokémon besides Wailord.
 * Steelix is the heaviest Generation II Pokémon.
 * Steelix has the highest base defense out of all Steel types and Ground types.
 * Steelix is the only non-Rock typed Pokemon that can learn Rock Polish while leveling up.