To unlock this achievement, you must collect all 12,00 gems
, 80 dragons
, and 12 eggs
, which unlock 100% game completion.
If you collect everything as you go through the game, you will end by rescuing the 80th dragon at the Gnorc Gnexus, unlocking this achievement and also opening the portal to the bonus level Gnasty's Loot, which is required for 120% completion.
Use your guidebook to see your completion percentage for each level. If you need help with some of the level, you can use this 120% video walkthrough: