Khorne felt a bit left out after the cocaine snorting slut glory hog all the Titan size daemon engines. Thus he decided to make a daemon engine far larger than that purple-skinned bitch and thus, the Skull Reaper was born. The Skull Reaper resembled a mechanical Bloodthirster with one arm bearing a chain axe and the other being a turbo-melta in which it first appeared in the Tome of Blood sourcebook for Black Crusade.
While we may have a rough idea on what it looked like, the lack of official artwork has forced some to kitbashed some custom analogue of a Khornate Titan. Some have ranged from the fucktastically, golden daemon worthy of awesome whereas others felt like it was made from cardboard and wet tissue paper, essentially speaking, it was pretty skubtastic at best.
Most have likened the Skull Reaper to look like a gigantic Kytan on steroids while some prefer it to look more like the Emperor Battle Titans of the Imperium. All in all, even though we don't get an official model or picture, it is sure as hell 500 times more awesome looking than the pathetic flamingo walkers of Slaanesh....*shudders in disgust*....