The Necrons in Warhammer 40K are a mysterious ancient species of humanoid robots that conquered the galaxy over 60 million years ago before overthrowing their masters and submitting themselves to the dormancy of their stasis-crypts. In Magic: The Gathering, black is the color that represents amorality and parasitism, so it's a perfect fit for the Necron legions.
Most of the best black cards from the Warhammer 40K Commander decks come from the Mono-black Necron Dynasties deck, but there are a few notable exceptions found in the Grixis (blue/red/black) Ruinous Powers deck. The Necrons are a long-forgotten people who gave up their flesh and their souls in exchange for near immortal physical bodies made of necrodermis and access to technology so advanced that it's beyond what a universe given 60 million years of growth is capable of emulating. Naturally, many of the Necron cards interact with artifacts in one form or another. But enough lore, let's take a closer look.
8 Tallyman Of Nurgle
Tallyman comes from the Ruinous Powers deck, but that doesn't make him any less powerful than his Necron counterparts. This 2/3 lifelink creature has a powerful ability in the form of its Seven-fold Chant which has you draw a card and lose one1 life at the beginning of your end step if a creature died this turn.
The life loss is more than paid for thanks to Tallyman's lifelink ability, leaving us with a creature that provides a relatively easy-to-trigger source of card advantage. Furthermore, playing a wrath and following with Tallyman will often result in the replenishment of your entire hand which is well worth the cost of seven life.
7 Illuminor Szeras
Access to large amounts of mana is a common way that Commander decks take over a game. Illuminor Szeras provides such access thanks to his Secrets of the Soul ability which allows you to sacrifice another creature and add a number of black mana to your mana pool equal to the creature's mana value.
While this might not seem like the best ability at first glance since you have to sacrifice your own creature, cards like Archon of Cruelty, and The Immortal Sun are all well-worth the cost of a creature to place on the battlefield early. Additionally, Illuminor works quite well with sacrifice-based deck strategies that often benefit from access to additional mana.
6 Triarch Praetorian
Triarch Praetorian is a good old aggressive threat that will provide you with value in the early game and the late game. A two mana flyer is a great creature to play early in the game as it is likely to get in for a fair amount of damage or eat a removal spell out of an opponent's hand.
Later in the game, you can either Unearth Triarch or use another means of reanimation to bring it back onto the battlefield to serve you once more. Its Dynastic Codes ability will then trigger, providing you with some card advantage in exchange for a mostly negligible amount of life loss.
5 Darkness
This is a card almost as ancient as the Necrons themselves. Darkness was last printed in Time Spiral Remastered all the way back in 2006. Despite this card being common, it hasn't been printed again until now, giving it a surprising cost of over $8.
The card's rarity isn't the only reason for its high cost though. Preventing combat damage, or a fog, is an effect that's normally only found in green and not even very often at that. Consequently, Darkness is a card that will always take your opponent by surprise: a pretty good way to snatch victory from the jaws of defeat.
4 Living Death
Living Death is a confusing card to read, but the long and short of it is that this card swaps the creatures on the battlefield with the creatures in each player's graveyard. As a result, this card is best put to use in a deck that's good at filling its graveyard with creature cards.
Thankfully for Living Death, there's more than a handful of such decks already in existence. Unfortunately, though, graveyard hate is also a fairly common piece of some Commander decks for this same reason. The upside of Living Death is that it's a great board wipe regardless since it forces each player to sacrifice the creatures they control rather than dealing damage to them. This gets around keywords like indestructible as well as most other abilities that would manage to escape your regular board wipe.
3 Out Of The Tombs
Speaking of good ways to fill your graveyard, Out of the Tombs is one of the best enchantments for doing exactly that. This enchantment mills cards from your library equal to the number of eon counters on it every turn, and it gains two eon counters every turn as well. It doesn't take a mathematician to figure out that your library will end up in your graveyard relatively quickly using Out of the Tombs.
However, that's strangely enough when the card is at its best. Instead of drawing and losing the game as you would normally do when you have no library, Out Of The Tombs skips your draw phase and returns a creature from your graveyard to the battlefield. This is an incredibly powerful effect, but it comes at the cost of you instantly losing the game if your opponent manages to remove Out of the Tombs or your graveyard.
2 Poxwalkers
Poxwalkers is a welcome addition to any Zombie tribal deck as it is both a Zombie and a creature with a built-in synergy for playing cards from your graveyard. Playing Zombie cards out of your graveyard is exactly what Zombie decks are all about, and that's exactly what Poxwalkers offers.
A match made in heaven to be sure, if such a thing can truly be said to exist in the grim dark fantasy setting of the Warhammer 40K universe. A Zombie can always dream. Oh, wait. Actually, they can't.
1 Biotransference
Given what you've learned about the Necrons so far in this article, you shouldn't be surprised to find out that the best black card in the Warhammer 40K decks turns all of your creatures into artifacts. Not only that, but all creature spells you cast become artifacts as well.
On top of all that, casting an artifact spell will now trigger Biotransference, costing you one life and providing you with a 2/2 Necron Warrior artifact creature token. This makes Biotransference one of the best ways to quickly generate an army of creature tokens that your opponents will be forced to answer. Just one more reason for Commander decks to pack a fair amount of enchantment removal. As if there weren't enough powerful enchantments running amok in Commander already.