Ekans is a purple, serpentine Pokémon. Its eyes, underbelly, the thick stripe around its neck, and rattle are yellow. Ekans has three pairs of black lines encircling its body, as well as another line that connects each slitted eye and curves toward its nose. Its large mouth has a round, pink tongue and no visible teeth.
Ekans moves stealthily through grass and preys on Eggs from Pidgey and Spearow nests, but can strike other prey from behind. It grows longer with age and wraps itself around tree branches at night to rest. If not in a tree, it will coil itself up—a position in which it can defend itself from all directions. Its jaw can detach to swallow large prey, but such a meal can make Ekans too heavy to move. A newborn Ekans's bite is painful, but not venomous. It flicks its tongue out to detect danger and the scent of prey. It was also shown to possess some swimming abilities. Ekans lives in grassy savannas and plains.
Ekans appears to be based on a boa and rattlesnake, and its facial markings resemble an Indian cobra's hood. However, its lack of teeth, ability to swallow large prey, preying on Pokémon eggs, and reaction to threats are more akin to an egg-eating snake. The yellow band around its neck may refer to the ring-necked snake. Ekans and Arbok may also be inspired by the legendary basilisk since they were originally the only Pokémon to learn Glare. The basilisk was said to be a poisonous, serpentine dragon that would kill people with its stare, which may explain Ekans's place in the Template:Egg3.