The Slaughterhouse is the new Gargantuan Warbeast that's coming for the Grymkin in Warmachine and Hordes. Privateer Press has started taking orders for this new, huge figure. They've also posted up a preview of its rules in both Hordes as well as in Requiem, their Iron Kingdoms RPG.
From the article:
And now… Something wicked…
…this way comes! The Grymkin Slaughterhouse is available to order! To celebrate this monstrous new addition to the Iron Kingdoms, I’d like to share with you a taste of what it will bring your tabletop, whether you’re playing it in WARMACHINE & HORDES or in the Iron Kingdoms: Requiem RPG.