When doing the puzzles for treasure chests, go to "Options" > "Exit Game" before completing the mini-game. You can repeat the puzzle again as many times as you wish until you get the item you want.

ACHIEVEMENT - HOW TO UNLOCK
Happily Ever After (30 points) - Complete the game.
PWNT! (5 points) - Defeat an opponent on your first turn during any single player game mode.
Cheating AI (5 points) - Be defeated by an opponent on their first turn during any single player game mode.
OMGHAX (20 points) - Make a match of 8 gems in a row in any battle game mode.
Epic Win (10 points) - Defeat an opponent while on 1 Life Point during any single player game mode.
Epic Fail (10 points) - Lose to an opponent while on 1 Life Point during any single player game mode.
Gate Hacker (20 points) - Use the Bash mini-game to destroy every locked gate, door or chest possible!
Save Verloren (5 points) - Save the town of Verloren from invading Goblins and Trolls. 
King Godd (10 points) - Defeat King Godd and complete the 'King Godd' quest.
Shadowbringer (15 points) - Defeat the Shadowbringer and complete the 'Shadowbringer' quest.
Dragonslayer (40 points) - Defeat the Green Dragon and complete the challenge quest.
Abominable (30 points) - Defeat the Yeti and complete the challenge quest.