Ratchet Bomb is a good sideboard against someone playing Esper Control or something else that can token bomb you.Same with Lifebane Zombie if you aren't going against green/white.

Shocklands are nice, but since this is monoblack, it would be a waste of money, life if you shock yourself, and could be better replaced with a swamp.

Personally I run a mono black aggro devotion deck that is fun, and there are some things you could splash in, like Rakdos Shred-Freak , a 2/1 haste creature for BB/RR that counts as 2 devotion. Same with Gift of Orzhova which can also be used with your shrine to Nyx to play stuff stolen with Nightveil Specter

Well, i got Pack Rat for rakdos shred-freak which is way better because it can win the game by it self.

''which can also be used with your shrine to Nyx to play stuff stolen with Nightveil Specter" i am planning to add some black/white scry lands. in order to play them.

I would like to see 2 Whip of Erebos in this deck for life gain. maybe drop the erebos god, and one devour flesh just to get some more devotion and lifelink going. Those extra 2 through 6 life gain will power underworld connections better. also works great to bring back merchant or even night specter. Desecration Demon loves to gain 6-7 life per swing to really put out aggro decks out of reach.

Well, i got whip of erebos in my mainboard because i find it more usefull than erebos. Instead i have dropped the pithing needle and added 2 erebos in my sideboard. I Just haven't updated it in tapped out :p. Thanks for the suggestion anyway