can somebody give me an opinion on my deck (MTG)?

It looks like some mean black control.

I would add more duress and maybe remove the physic miasma.

Throw Inqusition of kozelik in side bored for fast aggro players along with death mark.

Maybe put some royal assassins in for more control.

Put edges in side for control against manlands.

Throw more dread santuary in.

But all and all this is some good mean control.

I see that you are making a MBC(Mono Black Control) deck.

I suggest you try something like this:

MB

1 Liliana Vess

1 Sorin Markov

2 Grave Titan

2 Consuming Vapors

1 Memoricide

3 Mimic Vat

2 Inquisition of Kozilek

2 Mind Sludge

3 Gatekeeper of Malakir

3 Doom Blade

2 Disfigure

2 Duress

4 Sign in Blood

2 Dread Statuary

3 Tectonic Edge

SB

2 Consume the Meek

3 Memoricide

3 Sadistic Sacrament

1 Inquisition of Kozilek

3 Vampire Hexmage

1 Doom Blade

1 Duress