Arbok!!!!
Arbok (024) is a poison-type pokemon that evolves from Ekans. Because Arbok's type is poison, it is vulnerable to psychic and ground types, and is ineffective against steel.
Arbok's main strength is its strong attack. Its five most common moves are Poison Sting, Acid Spray, Acid, Gunk Shot, and Belch. The strongest of these moves is Belch. It can also use the special ability Intimidate, Shed Skin, and Unnerve.
Arbok's main weakness is lack of HP and defense, which can often outweigh its strong attack.
In some versions, Arbok can mega-evolve to Mega Arbok.
It does not evolve into Seviper. This common misconception stems from an error in the "Trainer's Choice" question on Advanced Generation Epsiode 77.