Loot Hero DX

This Achievement unlocks for buying one upgrade for any skill upgrade, Attack, Critical, Defense or Speed at one of the many houses you come across.

You can grind any level by killing enemies to get coins by going to the right side of the level and then back to the left side and the enemies will keep respawning just make sure that you don't kill the boss or else the level will end.

I show a coin grinding method in my Achievement Walkthrough starting at 2:01 minutes into the video.

At each of the Houses as you progress to the Right you can buy upgrades. Earn enough coins for one of them then press the according button (A, B, X or Y