There are only two black thrulls in the game so you might not want to go tribal, I would recommend instead just going with black good stuff and ways to abuse endrek sahr. If you put in a lot of creatures with etb effects, especially control effects like Shriekmaw, then you get a ton of use out of them seeing as you get their etb trigger, a number of thrulls, and the creature all by playing one card.
To abuse endrek sahr's tokens, I would recommend sac engines like Ashnod's Altar and Phyrexian Altar to turn your tokens into mana. By using cards like these you get the ability to play a creature, get some tokens, and sac the tokens to produce even more mana then you started with, possibly to play another creature and keep the chain going. Sac outlets also allow you prevent yourself from ever hitting 7 thrull tokens and keeping your commander alive. Skullclamp also seems like it would be great in this deck to produce massive card advantage.
You'll also want a few tribal cards like Coat of Arms to turn your thrulls from just utility and chump blockers into beaters. If you check out some mono black good stuff decks, mono black sac decks, tribal staple lists, and some token decks then you should be able to put together a solid deck.
I'm not a huge black player but tokens and toolbox strategies are what I'm best at and I feel like that's what would make this deck thrive compared to other mono black decks so just let me know if you have any questions.
October 8, 2016 1:12 p.m.
In Commander, there are in fact more than two black thrulls. There's Armor Thrull (one of my favorites), Necrite & Mindstab Thrull, Blood Pet, Basal Thrull & Blood Vassal, Exhumer Thrull, Thrull Champion, Thrull Parasite, Thrull Surgeon & Thrull Wizard... and that's pretty much all the good ones in mono-black.
I love thrulls, btw. =)
Also, check out this link for excellent tribal support: The Bones To Build Your Tribal Deck
October 8, 2016 6:09 p.m.
Sorry I'm not sure why but Starcity only showed me two mono-black thrulls when I looked them up. I still don't think it's a good idea though considering each thrull you play limits the number of tokens you can get without sacrificing endrek sahr, I just feel like it's not worth it.
October 8, 2016 7:17 p.m.
You sac Endrek's tokens to Attrition, or Ashnod's Altar, or Phyrexian Vault. And most of the card Thrulls have their own sac effects, so you put in Butcher of Malakir, Grave Pact, and Dictate of Erebos. Add in some creature recursion like Sheoldred, Whispering One and Hell's Caretaker. I can see good things happening with all this, though graveyard hate will not be your friend.