This seems to convoluted to actually work in my opinion. Try Summoner's Egg, Phage, and Harmless Offering/Bazaar Trader instead. I suppose you could keep endless whispers as a sort of backup plan/way to get your bazaar trader back though.
Unfortunately every try hard from Sacramento to Shanghai preaches from the top of their 27 lands + Mana Reflection that Tooth and Nail and Time Stretch are fine to play in the same turn but Armageddon is unfair.
It worked a few times for him. I would load up on more removal and tutors to find the endless whispers. Consider Dark Petition or Beseech the Queen as budget options. I know you're running the house guard for this, but these offer a bit more flexibility.
A card you may not have considered yet is Bronze Bombshell, with an active whispers and a sac outlet, this will bounce back and forth and kill your opponent pretty quickly.
Phyrexian Negator and Abyssal persecutor are both very aggressive cards, and while it seems like it would be amusing to make your opponent get stuck with one, they don't actually win you the game unless you're beating down with them. If they switch sides they could even kill you. I don't think they belong in this deck, unless you are ignoring the whispers and just trying to beat down with them. I would probably put persecutor in the sideboard to bring in if you want to transition the deck towards a more straight forward monoblack control for some matchups, and cut negator completely. Just my two cents.
other thoughts on these cards:
2 elixir of immortality - I don't think this belongs in this deck. Put it in the sideboard if you're worried about mill or burn.
2 nihil spellbomb - Again a sideboard card, this doesn't do enough for your deck to be in the main. You can also get this effect with a land and save space.
2 necrogenesis - Why is this even in here? You should embrace the whispers, not fight it.
3 moment's Peace - I like this card, but this is the main reason you're running green... looks like it would be better as a wrath effect. In black you have Mutilate (cheap and in mono-black is almost always a wrath), Life's Finale (cheap), Damnation (expensive, but the best), Crux of Fate (newish & cheap), Barter in Blood (cheap almost wrath), just to name the ones I can think of off the top of my head.
One more card that I have to suggest, just based on the cards you are playing, Disciple of Bolas seems like something you would like.
3 disciple of griselbrand
3 qarsi sadist
2 dimir house guard
2 phyrexian negator
2 Abyssal persecutor
2 phage the untouchable
2 Xathrid Demon
Spells (24)
2 elixir of immortality
2 nihil spellbomb
1 demonmail hauberk
2 necrogenesis
4 endless whispers
2 altar's reap
2 devour flesh
2 rite of consumption
3 moment's peace
3 culling the weak
4 jungle hollow
6 forest
10 swamp
2 devour flesh
2 life's legacy
1 moments peace
2 elixir of immortality
Still need help tuning deck.
So the plan is basically to set up endless whispers and phyrexian negator/Abyssal Persecutor/Phage the untouchable, and a sac outlet. then give these beaters with big drawbacks to your opponent. Use graveyard removal like necrogenesis to deny them sac outlets and getting your beaters returned.
My Decks:
All my Decks are budget
EDH:GRWHazezon TamarGRW, RKazuul, Tyrant of the CliffsR, BMikaeus, the UnhallowedB, UTalrand, Sky SummonerU, GRXenagos, God of RevelsGR, BGPharika, God of AfflictionBG
Standard:BMono Black Control(devotion)B- retired
Casual:UWHeroicUW, UGWall tribalUG, BPhylactery LichB
Modern:UBAbyssal PersecutorUB, WKnight TribalW
https://www.youtube.com/watch?v=bPdnDekGpgM
It worked a few times for him. I would load up on more removal and tutors to find the endless whispers. Consider Dark Petition or Beseech the Queen as budget options. I know you're running the house guard for this, but these offer a bit more flexibility.
A card you may not have considered yet is Bronze Bombshell, with an active whispers and a sac outlet, this will bounce back and forth and kill your opponent pretty quickly.
Phyrexian Negator and Abyssal persecutor are both very aggressive cards, and while it seems like it would be amusing to make your opponent get stuck with one, they don't actually win you the game unless you're beating down with them. If they switch sides they could even kill you. I don't think they belong in this deck, unless you are ignoring the whispers and just trying to beat down with them. I would probably put persecutor in the sideboard to bring in if you want to transition the deck towards a more straight forward monoblack control for some matchups, and cut negator completely. Just my two cents.
other thoughts on these cards:
2 elixir of immortality - I don't think this belongs in this deck. Put it in the sideboard if you're worried about mill or burn.
2 nihil spellbomb - Again a sideboard card, this doesn't do enough for your deck to be in the main. You can also get this effect with a land and save space.
2 necrogenesis - Why is this even in here? You should embrace the whispers, not fight it.
3 moment's Peace - I like this card, but this is the main reason you're running green... looks like it would be better as a wrath effect. In black you have Mutilate (cheap and in mono-black is almost always a wrath), Life's Finale (cheap), Damnation (expensive, but the best), Crux of Fate (newish & cheap), Barter in Blood (cheap almost wrath), just to name the ones I can think of off the top of my head.
One more card that I have to suggest, just based on the cards you are playing, Disciple of Bolas seems like something you would like.