For this achievement all you need to do is pull the sword from the stone in Alvesta. Alvesta can be found by following the map northwest and you will eventually find it, it is a town that is full of tree houses. The sword can be found on the other side of the lake from all of the tree houses. To pull the sword out you need to lick it and the walk backwards and jump a bit, when it comes out the mutator should be unlocked and your achievement should pop.
If you would like a guide of how to find Alvesta and the sword or a video guide for the whole achievement I have included my guide below