Here is the full list of all 31 Princess.Loot.Pixel.Again x2 achievements.
Beat Dark Warrior mission
Beat Dark Paladin mission
Beat Dark Thief mission
Find glory
Complete Warrior missions
Find the grail
Kill traitor
Complete Thief missions
Theft golden dagger
Save Princess
Complete Paladin missions
Kill a dragon
HA HA HA!
You are serious??
Kill rats
Theft crown
Collect 99 coins
Complete level without damage
Kill boss without damage
Blink!
Save a cat
Beat the boss
Find Fez hat, Meat cube and Scarf
Find Crying baby
Find the Guitar
Find Mush and Flower
Dead first time
Steal coins
Find secret place