To be able to get this achievement you will need 1st to beat the game to obtain the Contract of Reaper
After you obtain the book you will have to unlock it by spending 5,000 GEMS at the game over screen. It will be on the 2nd row the last item.
When you spend the 5,000 GEMS and unlock the contract just play and collect 1,000 GEMS from World 1 and after you have the 1,000 GEMS find a Reaper SHOP to buy it .
If you hit though the SHOP sign so it will be flashing then you can buy it for 990 GEMS.
Once you've purchased it you will unlock the achievement.