Nighthaze is cantrip for a single black mana, and comes recommended by my fellow Librarian Coatsy. A cantrip is a spell that has the line of text “Draw a card” after another effect. Cantrips are highly flexible cards and this one is no exception making it the Card of the Week.
The potential upside you can get from the single black mana this sorcery costs, can be game ending. Swampwalk is a keyword ability that makes the creature unblockable, as long as the defending player controls a Swamp. Additional information on Landwalk can be found here. This means that casting it on one of your Creatures will allow you to swing for certain damage. You can use this if you are playing Infect or just have a big creature, Nighthaze will allow it to attack for lethal. It has further utility when dealing with Planeswalkers, because Landwalk works on them as well.
The obvious downside is that your opponent needs to control a Swamp for this to be at its most effective. However, this is mitigated by Black’s popularity as a colour. Out of the current 20 top commanders 16 of them contain Black. The real downside is that it has to target a creature to resolve. Although it does not need to be a creature you control. If you just want to cast it as a cantrip and ignore the Swampwalk aspect, cast it on an opponents Creature there is very little downside. So at worst you spent 1 mana to draw a card.
Nighthaze would be a good addition to any deck running black that is looking to deal combat damage. Whether you are looking to punch through with a swole Rat from Marrow-Gnawer or just looking to let Skithiryx smash face.