Mono Black is still a thing! Although I've been considering splashing some white. But, let me start at the bottom and work our way up as I tell ypu how we win...
Ruthless Ripper
and Despise serve as our early game defense; Ripper's deathtouch can kill an irritating creature, and/or get some early damage in. Despise, of course, does some good hand-disruption to nip early plays on the bud. Bile Blight acts as minor removal, and Sign in Blood helps get the ball rolling a little faster.
On to mid-game! Hero's Downfall remove the irritating creatures and planeswalkers, permitting
Herald of Torment
and the all-important Squelching Leeches to lay the main smack-down.
Usually, by now, the opponent is about to lose; but, let's see if we can't make the bad scenario worse. Whip of Erebos gives us some late game recovery from the Herald's daily ping, and can get a previously dead creature out for a last hoo-rah. If we still have them, our various early to mid game stuff is still very much a factor: our Leeches are getting pretty big by now, and our removal can hit a surprise win-con (It was very satisfiying to watch Elspeth, Sun's Champion let off her ultimate, and quietly say "Bile Blight".) Finally, as a last resort, Gray Merchant of Asphodel can provide a final, dooming stroke against a stabilizing board state.
Our side-board helps recover from certain match-ups: Drown in Sorrow hits most token creatures, and
Silence the Believers
works against big, nasty creatures. Delve is a big thing in my area, so I have Tormod's Crypt to put a cork in it. (I sincerely hope nobody thinks to board
Rakshasa Vizier
for that...)
Dark Betrayal
is a must for other black-heavy decks, and Read the Bones is good against control and tempo match ups to get to my good stuff faster.