What the achievement asks
Defeat Mogul Razdunk in The MOTHERLODE!! on Heroic difficulty or higher. Ten points, both factions.
The MOTHERLODE!! is the goblin mine under Kezan, where the Venture Company is digging Azerite out of the wreckage left by Sargeras and trying to sell it.
The four encounters
| Order | Encounter |
|---|---|
| 1 | Coin-Operated Crowd Pummeler |
| 2 | Azerokk |
| 3 | Rixxa Fluxflame |
| 4 | Mogul Razdunk |
Mogul Razdunk is at the bottom of the mine and the achievement asks for nothing else, so the run is a straight descent.
Heroic or higher, but on one character
Blizzard's wording is "on Heroic difficulty or higher", so a Mythic or Mythic Plus run earns it just as well. There is no need to queue for Heroic specifically.
The eight Heroic dungeon achievements are not account-wide. Four on your main and four on an alt leaves you with nothing. They all have to be earned by the same character.
Once one character holds all eight, the Battle for Azeroth Dungeon Hero achievement they feed into is account-wide, so the grind only has to happen once.