Mechagon is a heretofore unexplored part of Gnomish lore in World of Warcraft, having not been mentioned before its inclusion in the game with patch 8.2 and having no lore leading up to it. Or, more accurately, no lore prior to a new comic that outlines one scarred Gnomish explorer seeking out the ancient legendary realm of Mechagon, something so shrouded in mystery that no one else even believes it’s real.
Also that no one has apparently ever mentioned before now even in the context of a legend, but let’s not quibble.
The comic is free for anyone to peruse and details the journey of Kervo as he struggles to find Mechagon and prove that it’s real… although he may not walk away with the proof that he had hoped to find. You can check it out now if you’d like a little more backstory before you go run around within the mechanical realm.