To have the ability to interact with the stack, or at least cast spells on opponents turn, is important. Unfortunately this is not one of the strengths of the color black. Still, there are a few cards that at the very least can make your opponent stumble at the wrong moment.
The following cards are instants, and cost B or less.
Misinformation. This card looks good, literally, which is the main reason I will test it tomorrow. However it does some crazy things against my poor match-ups like combo and UW control.
Those decks rely on cards not suddenly move around at the wrong moment. For example, when the storm player activate LED after playing Past in flames he expect the rituals to be in his graveyard, and not on top of his deck. Then there is the typical blue cantrip deck. Brainstorming becomes a time walk if all the see is cards that was in the graveyard a moment ago. Preferably expensive cards, or those of marginal value like Daze.
It is also nice vs Dredge.
Next is
Archive trap.
A blue spell that can be cast for zero mana if your opponent search his library the same turn.
Iirc that is what you do when fetching, right?
Or play enlightened Tutor. Or use any of the many search effects that exist in legacy today.
The idea with this spell is the same as above; to disrupt the opponents timing. Main advantage is the casting cost of nil,nada,zero. The surprise value should be great first time.
Funeral charm. This card need no presentation. It has several useful abilities but those are weak on their own. What makes it worth playing occasionally is that it is the only instant speed discard there is, afaik. To force a combo player discard a card at the wrong time, for him, can make "all the difference in the world, Mr Freeman".
Disruption is not only discard and counterspells. Misplacing peoples stuff tend to make them upset too.