Pokémon Clip'n'Go Poké Balls Tentacha & Tauchball

Tentacool is a small, cnidarian Pokémon. It has a light blue, clear body with two large, transparent, red crystals on each side of its body and one small one in the middle. Near the base of its body is a pointed, beak-like projection and two eyes with small pupils. There are two grayish tentacles extending from beneath its round lower body, which has a cape-like formation on the back.

Tentacool's entire body is made of 99% water, and the remaining 1% contains the organ that produces its poison. It absorbs sunlight and refracts it using the water inside its body to convert it into beam energy. Its tentacles are laced with stinging cells and, as seen in the anime, it can control Pokémon it touches with its tentacles. The tentacles break off occasionally, but they can regenerate. The poison from its tentacles is so potent, that someone would need to be immediately rushed to the hospital. Tentacool is not a very strong swimmer, traveling throughout the world using ocean currents. Tentacool searches for food while drifting on the surface of shallow seas. Tentacool can blend in the water, making it very difficult to spot. It will sometimes wash ashore and shrivel up due to dehydration, though it remains equally as dangerous. Tentacool may be revived if thrown back into the sea.

Tentacool is mistakenly believed to be a species relative of Toedscool; in actuality, the two Pokémon are biologically unrelated.

Evolution
Tentacool evolves into Tentacruel.

(Source: Bulbapedia)