The following Sunken Treasures become unlocked when you complete the corresponding task.

Anchor:
Won from a Bronze Chest.

Arcade:
Unlocked by playing 100 games in a row.

Candy:
Unlocked by having 500 Candy at one time during the Spooky Shark event (Oct. 15 - Nov. 2).

Cannon:
Won from a Silver Chest.

Coin:
Unlocked by having 1000 coins at once.

Cookie:
Unlocked by having 500 Cookies at one time during the Santa Shark event (Dec. 11 - Dec. 31).

Crate:
Won from a Bronze Chest.

Cthulu Plush:
Won from a Gold Chest.

Cutlass:
Won from a Silver Chest.

Dubloon:
Unlocked by having 100 dubloons at once.

Gravestone:
Won from a Gold Chest.

HoZ:
Won from a Silver Chest.

Jack of Hearts:
Won from a Gold Chest.

Lasergun:
Won from a Gold Chest.

Lx0:
Unlocked by scoring 100 or more points in Sink or Swim mode.

Mana:
Won from a Silver Chest.

Meteor:
Won from a Bronze Chest.

Pirate Flag:
Won from a Silver Chest.

Present:
Unlocked by scoring 100 or more points in any game mode during the Santa Shark event (Dec. 11 - Dec. 31).

Reaper Doll:
Won from a Silver Chest.

Rocketship:
Won from a Gold Chest.

Seaweed:
Won from a Bronze Chest.

Shark-o-Lantern:
Unlocked by scoring 100 or more points in any game mode during the Spooky Shark event (Oct. 15 - Nov. 2).

Shipwreck:
Won from a Gold Chest.

Space Pal:
Won from a Gold Chest.

Statue:
Wait for 1 minute at the 'Title' screen before starting a game, then crash without scoring any points.

Stone of Balance:
Won from a Gold Chest.

Treasure Chest:
Won from a Bronze Chest.

Treasure Map:
Won from a Bronze Chest.

Trident:
Won from a Silver Chest.

Vase:
Won from a Bronze Chest.