Ring of Pain

Spinebacks are very common in dungeons past level 2. They have two forms - a spiny, dangerous form that does heavy thorns damage when attacked, and a more docile form with its belly exposed and has no thorns damage. It changes forms every couple of turns. If you don't have access to reliable freeze status (which prevents the thorns damage), I would recommend softening up the spineback when it's in its docile form, then going for the kill after it reverts. Try not to hit it more than once in its spiny form because it hurts a lot. You can prepare for this with poison, petrify, and/or a high health stat.