Evolution. Ekans evolves into Arbok at level 22.

How do you evolve Ekans into Arbok?

Arbok is a Poison-type Pokémon. It evolves from Ekans starting from level 22. It can Mega Evolve into Mega Arbok using the Arbokite.

Is Arbok a good Pokemon?

Arbok has subpar offensive stats, and it is rather frail, which means that just about any super effective attack—or even a strong neutral one—will OHKO it. However, it is a good setup sweeper thanks to its access to Coil, and while it isn't inherently bulky, it has a good defensive typing.