Omega: Deltascape v4.0 Savage is the final encounter available in Final Fantasy XIV: Stormblood's v4.05 update. This battle features Exdeath, a major character from Final Fantasy V.
Exdeath on Savage difficulty drops ilvl 340 token gear, in addition to providing the most powerful weapon in the game.
Below is a full guide to the encounter. First we will describe the abilities for both forms of Exdeath before going into his rotation.
Note that after you kill Exdeath, for the rest of the lockout you will start at Neo Exdeath. You must wipe after Neo Exdeath is targetable for this to happen. Neo Exdeath does not auto attack, and will reset aggro completely periodically.
For a full guide, check out Kiri Kotone/Yume's guide to Deltascape v4.0 here.