One of the things I always liked about flicking through the Witch Hunter codex was the Retributor squad, since whilst most people would call them "SOB Devastators" they actually pose a difficult choice. The only heavy weapons they can take (from memory...) are Multi-Meltas and Heavy Bolters. Personally, I'm not keen on a full squad using Multi-Meltas, not keen on the weapon at all really... I prefer to have the mobility when it comes to anti-tank weaponry and such....
So for my Retributors, I wanted to take full advantage of the Act of Faith which gives you AP1 on a 6. I figured by pumping out a shedload of Heavy Bolter shots with them, they could absolutely maim pretty much anything coming towards them - Terminators, Monstrous Creatures and such. Even just drag down threatening vehicles through weight of fire.
These guys were made from the cloaked Dwarf Thunderers and given shoulder pads to bulk them out a bit more. I'd imagine they're the lazier (and chubbier) Brothers of the Forge, who prefer to let the enemy do the walking.
Also, Retributors can take an Immolator as a dedicated transport, which means effectively, 2 heavy support slots for the price of 1, and I can use the Immolator to be transporting another unit from the first turn, or roving around on it's own as a battle tank.
I realised now in uploading this, I planned to add an Imagifier to the squad, to help ensure the Act of Faith goes off when I want it to. So I'll build and paint that chap over the weekend, along with the Immolators.