The Mechagonian Threat

If you're here after the release of patch 9.1.5 and are wondering why your achievement completion tooltip still says you need Operation Mechagon - The Mechoriginator to complete The Mechagonian Threat -- even though Blizzard's patch notes say that the dungeon requirement for Allied Races like this one have been removed -- it's because that's only partially true.

You don't HAVE to actually complete the dungeon, but you DO have to go to Mechagon and talk to Prince Erazmin and grab this dungeon quest. After you grab the quest, talk to the NPC again, and you should see an available skip dialog to complete the quest without doing the dungeon. You can then proceed with the questline to unlock the Mechagnome race.

To reach the first quest of this chain (The Legend of Mechagon) you have to complete the Patch 8.2 intro quest line (25 quests). It's started with The Wolf's Offensive (autoaccept on level 120), through the Hearth of Forge quests in Silithus and Highmountain, and up to A Tempered Blade where you unlock [faction=2400] as allies in Nazjatar. For more info, check the [guide=8197].

You must accept the quest from the NPC and talk to him again to skip the dungeon requirement.