Warning: spoilers ahead for Dark Nights: Death Metal #7!
A suit can really make the man, especially when it's a suit worth billions of dollars, invented by a once-in-a-lifetime technological genius, and constructed for the express purpose of taking down the strongest being in the world. Such a distinction most famously belongs to Iron Man's Hulkbuster armor - the huge, hardcore enhancile suit designed with the intent of going toe to toe with the Hulk. But over in the DC Universe, there's a far deadlier genius hunting even bigger game, and he just proved he has the suit to back it up.
Lex Luthor has long hated Superman, but the events of the recent Dark Nights: Death Metal story have forced the two to work together against common foes. Thankfully for Lex, one of those foes is the Last Sun, a superman from the Dark Multiverse, meaning that Metropolis' richest man may not get to swat Clark Kent like a bug, but he still gets to kill one version of his longtime nemesis. Happily for fans, in doing so Lex reveals his own version of Hulkbuster armor, and proves it could take down the Man of Steel in moments... as long as Lex doesn't mind going down with him.
In Dark Nights: Death Metal #7, by Scott Snyder, Bryan Hitch, Yanick Paquette, and Greg Capullo, the Last Sun fights the entire Superman family, easily withstanding their attacks. That's when Lex arrives in the suit he refers to as his Sunday Best. After being booted from his job as second fiddle to Perpetua, the genius decides to put his smarts to good use and create a super suit powerful enough to stand up to the powers of Superman’s evil doppelganger. It’s not the first suit that Luthor has used to fight Superman, but this version just may be his craziest. Powered by a black hole, the suit is super-powerful, but so volatile that any damage would cause a meltdown... which is exactly what Lex is counting on.
Already fighting high above earth, tumbling somewhere in the atmosphere, Luthor self-destructs the suit, releasing the black hole and destroying the Last Sun in the process. The mechanics of a black hole - sucking in light and matter - makes it a perfect way to ax someone whose powers are derived from sunlight. A black hole is already destructive enough to pose a risk for Superman, but in specifically robbing him of his energy source, it's the perfect way to take him down - especially in the form of the Last Sun.
Taking Superman down usually requires top-level invention, so it's not surprising Luthor needs a suit to do the job. Batman has also used his money and mind to create armor specifically to fight both Superman and his Justice League teammates. Batman's famous armored anti-Superman suit appeared in The Dark Knight Returns by Frank Miller and Klaus Janson, while the Justice Buster Batsuit was used in Scott Snyder’s Batman: Endgame to take out the Joker Toxin-corrupted Wonder Woman, Flash, and Aquaman, but ultimately failed where Luthor succeeded in taking out Superman, despite miniature red suns in the suit's knuckles.
Dark Nights: Death Metal has been a huge, bombastic story, so it's fitting that its finale includes a hugely powerful Hulkbuster-style suit that ends the corrupted Superman for good without needing to be a factor in future stories of clashes between DC's greatest hero and its smartest villain. Lex Luthor is often overlooked when discussing awesome comic-book villains since he has no inherent powers, but moments like this serve to underline just how cool he can be when the right writers and artists harness his potential for destruction and conquest.