Here is the full list of all 30 Nightmares from the Deep 2: The Siren's Call achievements worth 1,000 gamerscore.
Finished a game of Mahjong in less than 1 minute.
Finished all the games of Mahjong.
Finished half of all the games of Mahjong.
Completed the bonus adventure.
Completed the game.
Completed the game on expert difficulty
Got to the contents of Davy Jones' chest.
Gathered a twelve golden fish tokens.
Finished all the puzzles without skipping
Finished all Hidden-Object Scenes.
Found all morphing parrots.
Got to the top of the lighthouse and saw what's underneath.
Found all hidden octopi.
Enabled your ally to return to work.
Prepared a spiked coffee.
Found your way inside the lighthouse.
Finished 10 Hidden-Object Scenes in a row without using any hints.
Fixed the radio.
Found all secret sea horses.
Entered the shipwreck cemetery.
Finished a Hidden-Object Scene in less than 1 minute.
Found 4 Hidden Objects within 4 seconds.
Saved your ally from a tight spot.
Found a direct way to get behind the closed gates.
Finished any Hidden-Object Scene with less than 3 mistakes.
Finished 5 puzzles in a row without skipping.
Visited a local bar.
Finished a puzzle in less than 1 minute.
Witnessed the devastating attack of the sea monster.
Arrived on the pier.