Octopus Pig

The Octopus Pig (aka Octopig) is a Pig with octopus tentacles that appears on the Piglantis loading screen. He is not seen in any levels of the game, just on the loading screen. On the screen, he is seen stealing an egg from Red and Bomb. He was most likely a costume, so it's possible the pigs either dumped it off screen after getting the eggs, or the birds destroyed it off screen.

In the Angry Birds Toons: Season 2 episode "Sweets of Doom", King Pig becomes an octopig after eating some radioactive candy while he and Bubbles were pursuing a piece of dropped candy into the castle dungeons. At the end of the episode, several pigs eat radioactive candy and become octopigs themselves, while Bubbles becomes an octobird after the camera irises out when he too eats the radioactive candy.