Risky Ring - ring in high demand
This is one of the most useful rings for classes that rely on large number of attack rolls, these include:
The big downside is that Saving Throws have a Disadvantage, that could leave you prone to various debilitating effects. For this reason, evaluate if the character that wields it can sustain effects like Fear, Charm, etc.
Location - Risky Ring
Even though the ring takes many of the builds to the next level it is very easy to obtain. It is found in Act 2 Moonrise Towers. Be sure to to infiltrate the tower first, and not attack the Absolute forces.
Look for Drow trader named Araj Oblodra. She is the ones selling it.