One of the strongest Unholy fights this tier. Never let your Necrotic Plague drop, ever. Constantly extend throughout the fight, mass spam Blood Boils when imps spawn and use Gorefiend's Grasp to stack them under the boss, spread your diseases to the Voidfiends, and watch yourself dominate the meters. You can pre-cast AMS when the boss is casting Fel Surge and the debuff won’t apply to you, therefore you never have to run out. Just keep extending your diseases and spread them around. Plague Leech off of adds on CD to get free runes, and make sure to Soul Reaper Vanguard Akkelion + Omnus when applicable.
The reason why Plague Leech is the desirable talent on this fight is because with the pace of the fight, there’s never actually any time you want your Necrotic Plague to fall off. You’ll constantly have something to spread it to, whether it be imps or voidfiends. You might as well take Plague Leech to get some rune return off the adds when applicable, and your NP will already build to 15 stacks before any adds spawn in the fight anyways.