From Diablo Wiki
The Vengeful Eye is a special quest item that is required as part of the Infernal Machine event in Diablo 3 classic. This item can not be found in Reaper of Souls, though old D3v Writhing Spines can be used in RoS, but only to obtain the organs to craft the D3v version of the Hellfire Ring.
The Vengeful Eye is a special object that can only be obtained in the Realm of Turmoil, as part of the Infernal Machine event. Players must battle uber versions of Siege Breaker and Zoltun Kulle for a chance to obtain the Vengeful Eye.
Players must have five stacks of Nephalem Valor for the Vengeful Eye to have any chance to drop. Even then, the odds are fairly low, and can only be increased with higher levels of Monster Power. Magic Find does not affect the odds in any way.
Vengeful Eye odds:
- MP0 = 5% chance to drop.
- MP1 = 10% chance to drop.
- MP2-10 = 10% better chance with each level, up to 100% chance on MP10.
Video of the battle from the Realm of Turmoil.
Obtaining a Hellfire Ring
- Obtain the three keys and the Infernal Machine plan for the Blacksmith.
- The Key of Destruction will drop from Odeg the Keywarden in Act I - Fields of Misery
- The Key of Hate will drop from Sokahr the Keywarden in Act II - Dahlgur Oasis
- The Key of Terror will drop from Xah'Rith the Keywarden in Act III - Stonefort
- The Blacksmithing Plans will drop from Nekarat the Keywarden in Act IV - Gardens of Hope 2nd Tier
- Craft three keys, one of each, into the Portal Device.
- Activate the Portal Device inside of the Heretic's Abode to create a red portal to one of the three Realms:
- Take the three demonic organs to Haedrig and craft them into a Hellfire Ring.
Note that steps 1-3 must be repeated multiple times, since you must create at least three red portals to obtain all three demonic organs.