It is a Fel Reaver Iron Horde version, and the original Fel Reaver is literally a machine powered by fel energy and held together by magic - and Iron Horde technology comes from Blackfuse (the merc Goblin that worked for Garrosh on SoO), so the Archimonde mount and Iron Reaver Boss is a evil shredder powered with fel magic from hell with a goblin engineering touch lol