This is story related and cannot be missed.
You get this for beating the final boss in Dungeon 9
Boss has 3 stages
- teleports around + melee hit (you can hit him after dodging his hit)
- Teleports around and turns you to stone with magic orbs (dodge orbs, same as before... Hit him after his slash misses you)
- Here and there he will turn into goopy puddles... Dance around them, can't damage him
- Final stage is the big ugly alien monster. Hit the eyes when they are open while dodging vines and killing spitting flowers... Not hard at all