Spiral Knights content update from Three Rings. More specifically, the game features new Shadow Lair boss zones, which in turn feature big baddies with names like Lord Vanaduke and Snarbolax (yep, that's really his name, Snarbolax).
Players who recover iron lockboxes have a chance to find shadow keys which can then be used to unlock one of several express elevators that lead right into the depths of the Shadow Lairs. The bosses themselves will provide "trickier, tougher boss fights [and] will challenge even the bravest, boldest, and best-equipped knights, presenting the greatest challenges the game has seen so far," according to a new Three Rings press release. There's more info available on the official Spiral Knights forums, and you can download the game via the official website.