Piglantis

Piglantis is the twelfth season in Angry Birds Seasons and the third in Season 2012. It was released on June 14 with other platforms such as PC, which is the second Summer-themed episode, the first being Summer Pignic. The new feature in the game is buoyancy: birds (except Bubbles for some reason), glass, and wood can go in the water and are light enough to be pulled back out of water. Pigs and stones are too heavy to come back up and will sink down until they touch the bottom. Pigs can stay underwater for only a short amount of time before they run out of the air and the pigs are defeated.

This update gave Trick or Treat a new ending cutscene. The Haunted Hogs update added Angry Birds fishing lures into the background. The Bad Piggies turned slightly different in appearance, as did the color of Mighty Eagle and pause buttons.

The chapter also reappears as the seventeenth chapter in Angry Birds Reloaded, adding 15 more levels.

Storyline
The following is from The World of Angry Birds Official Guide, as told by the Mighty Eagle:

THE LOST CITY OF PIGLANTIS

''Long before I was even hatched, there were stories of a legendary lost pig city somewhere to the south of Piggy Island. No one knew where it was for sure, or even if it existed, but everyone knew its name - Piglantis.''

Angry Birds Reloaded
Red, Chuck and Bomb are on a beach when out in the distance, a Minion Pig in a mermaid costume stands on a rock. Red and Bomb are disturbed by this, but Chuck seems to take interest in the pig's activities.

New Features

 * Water:
 * Small and Medium Birds will float, but bigger birds will sink, along with Bubbles' inflation.
 * The bird's special actions can be activated underwater including Hal, although his ability is useless underwater.
 * Small pigs will float in water and big pigs will go down.
 * The egg that Matilda shoots will not explode if it hits the water. Instead, the ocean current drifts it until it hits an obstacle. The Egg can also explode under the water if it hits the ocean floor or obstacles found under the water (Ex. Seashells, Starfish, Coral, & Blocks).
 * TNT will also work for underwater structures
 * If a Bomb explodes underwater, the explosion sound effect will be muffled.
 * New Objects.
 * Mermaid and Fishes pigs come in this episode.

Golden Eggs

 * There is a Golden Egg in level 2–4. You must use a Matilda to destroy the coral and then Terence to get it underwater.
 * Get all 3 stars on every level.

Trivia

 * Before the episode colors were removed in an update, the representative color they used in Piglantis is kelly green.
 * This episode's name is a pun on the fabled underwater city of Atlantis.
 * The Octopus Pig is on the loading screen, even though he wasn't in the episode.
 * The theme has changed on the update of Back to School, making Piglantis the fourth episode to have 2 different theme songs, with the first two being Moon Festival and Hogs and Kisses, and the third being Year of the Dragon and 5th being Winter Wonderham.
 * It is alike to Pig Dipper in Angry Birds Space.
 * In the files of Angry Birds Seasons, Piglantis is occasionally referred to as "Movie." There is also unused data in it referring to caged animals, monkeys and a hunter. Alongside that, the loadlist in v2.4.0 of Angry Birds Seasons HD mentions "INGAME_MADAGASCAR_CHARACTERS_1".
 * Going by this, it's likely that Piglantis was originally planned to be or replaced a Madagascar collaboration, seeing how Madagascar 3: Europe's Most Wanted released later in 2012.