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