The following contains spoilers for Storm & the Brotherhood of Mutants #3, now on sale from Marvel Comics
One of the most entertaining elements of Sins of Sinister has focused on the grim incarnation of the X-Men who've embraced Sinister's mentality. As a result, the mutant empire has converted plenty of powers into new tools, and retrofitted mutant clones into pieces of their terrifying inventions. The latest takes things to an entirely new level and gives a major figure in this timeline their most impressive ride ever.
Storm & the Brotherhood of Mutants #3 (by Al Ewing, Alessandro Vitti, Rain Beredo, and VC's Ariana Maher) introduces Emma Frost's personal mech, the Blood Diamond Monarch. The giant robotic suit is dangerous enough that it helps ensure the destruction of Storm's Brotherhood, even if it can't withstand a fully unleashed Omega-Level assault. Even compared to other Marvel mechs though, the Blood Diamond Monarch is an impressive (and dangerous) creation.
Sins of Sinister Gives the X-Men's Emma Frost Her Own X-Mech
By the events of Storm & the Brotherhood of Mutants #3, almost the entire universe has either become consumed by or fallen under the boot-heels of the Red Diamond Empire. Atop that imperial version of Krakoa is the Sinister version of Emma Frost, a ruthless and cruel killer who continues to wipe out life across the cosmos in the name of protecting her "students." Wading into open conflict with the remnants of Storm's Brotherhood left behind centuries after Ororo's death, Emma isn't content to just sit from the sidelines and command her forces. Instead, while her Chimera forces assault the Brotherhood's stronghold, Emma connects directly to a giant new robotic body.
Comparable in size to entire planets, the Blood Diamond Monarch is a giant mech, constructed of pure diamond, that Emma can pilot directly into battle. Based on designs for Master Mold, which has been redubbed the Mistress Mold, the Blood Diamond Monarch comes equipped with a giant diamond whip that allows her to strike with such power that it can cause a "sun-quake" in the Brotherhood's citadel. Effectively a diamond sentinel, the weapon is powerful enough to overwhelm the Brotherhood and almost wipe them out. They only survived due to the intervention of a resurrected Storm, who sacrifices her life to draw enough lightning from across the universe to destroy the Blood Diamond Monarch.
How The Blood Diamond Monarch Compares To Other Marvel Mechs
Even if the mech only lasted one issue, Emma's X-Mech is just the latest wild turn in the Sins of Sinister timeline, and one that fits within the story's embrace of sci-fi tropes. The Blood Diamond Monarch seems far more designed specifically for offensive purposes than some of the armor built by Iron Man, which served more specific purposes (such as his Celestial Buster Armor). The Monarch is easily able to strip away the defenses of the Brotherhood's base and might have been able to wipe them all out alone. This suggests the mech might not have the greatest defenses, sacrificing durability for other purposes.
The Sentinel-inspired design of the mech speaks to the Sins of Sinister's embrace of villainous tactics, cannibalizing the technology of the mutants' enemies to create their newest weapons. Compared to other Marvel mechs introduced over the years, the Blood Diamond Monarch is one of the most impressive. While the Spider-Mechs featured in "End of the Spider-Verse" like the Leopardon are impressive, the Blood Diamond Monarch being operated by telepathy and coming with the support of Chimeras might make it a more ferocious threat. It might not reach the scale of the Galactus-style Iron Man from Avengers Forever, but the destructive nature and vicious goals of the Sinister Emma might make the Blood Diamond Monarch the most actively dangerous Marvel mech.