As a Pokémon expert, I can tell you that Onix, which is a Rock/Ground-type Pokémon, does not typically evolve through traditional means like leveling up or using a specific evolutionary item. Instead, in the Pokémon games, Onix can evolve into Steelix under certain conditions.

In the main series games, Onix evolves into Steelix when traded while holding a Metal Coat, an item that can be found in various locations or obtained as a reward in some games. The Metal Coat is not consumed in the evolution process.

Here's the evolution process in English:

Onix evolves into Steelix when traded while holding a Metal Coat.

And the translation in Chinese:

隆隆石（Onix）在持有金矿石（Metal Coat）的情况下进行交易时会进化成大钢蛇（Steelix）。

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2 Answers. Onix doesn't evolve into Steelix by leveling up. You have to trade Onix while holding Metal Coat. Steelix can also be found in the wild.read more >>