This included a group of various murlocs who inhabited an island's cave on the island. Sen'jin said that the murlocs were once peaceful until recently. They are found in the Blizzard-made "Prologue campaign" called Exodus of the Horde which comes with the Frozen Throne Expansion pack in Warcraft III. They are also found in the Warcraft III: Reign of Chaos demo's "Prologue". They worshiped Sea Witch and sacrificed prisoners taken from their dungeon because Sea Witch told them if they did not she would sink their island. Their society was highly organized compared to other murlocs with buildings that made fighting units, heroes, and attack tower buildings. They seem to have a high tolerance for heat, because their hero is fire-enchanted and their cave home was burning with fire and lava. Murloc High Sorcerer seemed to be their leader, under Sea Witch.
They captured members of the Orcish Horde, Darkspear tribe, and Kul Tiras Marines. Thrall managed to break out and free the Horde and Darkspear prisoners (all but Sen'jin). The Kul Tiras prisoners attempted a break out, but were unwilling to cooperate with the Horde and so were outnumbered, isolated, and killed by the murlocs. Thrall was too late to help Sen'jin, who was killed by Murloc High Sorcerer. Enraged, Thrall and his troops destroyed Murloc High Sorcerer. The Underworld Minions tried unsuccessfully to prevent Thrall's escape from the island.
Other Underworld Minions included a Ghost Spirit, ghosts, a Tome Wraith, sludges, skeletal archers, giant skeleton warriors, black spiders (led by Black Widow], salamanders, salamander hatchlings, mud golems, rock golems, and various gnolls including Gnoll Gold Miser. Any land-dwelling minons likely met their end in the sinking of the island, although they could have all lived in the underground complex. Sea Witch seemed not to worry about the island sinking either.