Loot Hero DX

This Achievement unlocks for fully upgrading one of your skills to level 10. 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.

Loot Hero DX - 100% Full Game Walkthrough.