Rings that say their effects don't stack, mean that their
effects don't stack with effects from similar rings, but will
stack with similar effects from other sources. Re-rolls,
however, never stack regardless of the source.
Blessed rings can have up to two different enchants on them
instead of one. Some blessed rings can have additional benefits
such as stronger bonuses or weaker penalties than they would
Cursed rings have no additional harmful effects besides the
usual penalties (see Cursed Items).