Tentacruel has only a few differences from its pre-evolved form. It now has 14 long tentacles. It also has a beak; the mouthparts are on the front and back of Tentacruel's head. Also, as seen in the image above, Tentacruel has Two Huge eyes below its head.
Tentacruel can have the ability Clear Body or the ability Liquid Ooze. Clear Body prevents the opponent from lowering any of Tentacruel's stats. Liquid Ooze damages any opponent that tries to drain Tentacruel's HP. With 80 tentacles for ensnaring victims, it prevents escape until the prey is weakened by poison.
In the anime
During Tentacool & Tentacruel, Team Rocket causes a Tentacruel to grow to an enormous size, wanting revenge on the destruction of its home, it goes of to destroy everything in its path, but Misty manages to stop Tentacruel and saves the day.