Backpack Hero

By far the easiest way to get this achievement is using a good charm build centered around burn, poison, and spikes. Use armor and shields to boost up your guard to not take damage. Try to find a good shield that adds spikes or can be smithed into having spikes. The relic that lets you keep half your armor after your turn ends is very helpful to keep your armor up. I found some good instruments like electric guitar and harp boosted their damage or added damage with blacksmiths. If you want a very easy time in the third section choose the frozen heart zone because this type of build is a perfect counter for any of the hard enemies that you will find there. It’s so perfect in fact that if you can get the last boss there and get her charmed on her turn by using burn and poison she will actually just run away and you will not have to worry at all about her 2nd phase of the fight. Charm is just that broken in this game.