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