Obsidian jaguars

The Obsidian Jaguars are from an unknown Founding whose chapter world is overrun by orks, leaving them up in the air on numbers and capabilities. Their Fortress Monastery called "The Sabre" got destroyed by orks of the Goff Klan while most of them were away doing what marines do best, and before they could return to save their club house the Space Yiffs tried to step in but were also too late. They salvaged what little they could before they kicked over the fort so the green kids couldn't still play with it.

This happens in 8th Edition with a mention in The Saga of the Beast, as well as in White Dwarf and the short story Psychic Awakening: The Stand of the Sabre.

They're essentially Aztec themed Space Marines that decided to black out all the intense colors, so they're a delight for those that are good at modelling but suck at painting.

Behold, a Chapter that is made only slightly harder to paint than Iron Hands by the addition of one detailing color.

With the plethora of 3D printing options showing up you can add a ton of cool bits to this army to make them slick looking regardless of pigment.