I was wondering if it is possible for the ring wearer to take no damage if he is, say, a monk with evasion to take no damage at all.
PRD text of Ring of Retribution: "Once per day, the wearer of this charred bone ring may, as an immediate action, cause it to detonate in a 30-foot-radius burst that deals 10d6 points of fire damage (Reflex DC 14 half). If the wearer is killed by the detonation, all magical equipment he carries must also save or take fire damage, and all nonmagical equipment takes this damage with no saving throw. This explosion never destroys the ring."
I'm just wondering if it's possible to create a pseduo leeroy jenkins build with evasion and high reflex saves to be a walking bomb.
Nothing says the effect of the Ring of Retribution doesn't work like every other reflex save effect. It might seem silly to be able to evade your way away from an explosion centered on you, but if it wasn't suppose to be possible it would have a clause similar to the Detonate spell (which is that you automatically take half damage but receive no saving through).
The real question is how you'd fluff it, though! Personally, I'd imagine it looking similar to what you'd see when a monk's spell resistance isn't overcome by a Fireball spell, with his body glowing faintly as the flames simply fail to scorch his warded flesh. Of course, that's not really a dodge like you'd expect a reflex save to be, but... Well, I'll chalk it up to gameplay and story segregation.