The dungeon at the west coast of the main continent. Its Keeper was unknown, but supposedly weak, with only one dungeon heart and in a heavily populated area brimming with adventurers. Hir favoured skeletons as an attack force, making hir likely a follower of Crowned Death.
The town closest to it is an unnamed citadel-like city towering 8 kilometres downstream over the river delta, bristling with ships and docks. It is surrounded by a wall with active measures preventing ships to enter via river at night.
The river disposed of the immediate corruption of the dungeon upstream from the city, with probabe ill effects for the towns inhabitants.
Attack on the DungeonEdit
Prior to Mercury's attack on the dungeon she prepared with extensive intelligence and scrying. This allowed her to build a liquid replica of the dungeon in her command centre for tactical purposes.
She once again led the actual attack with a possessed ice golem. Her invading force, consisting of thirteen more ice golems, three of which also with senshi transformation enchantments. Divided in three groups Ami invaded the dungeon chosing the avenue of attack the enemy Keeper probably had in mind in regards to the city - by the river bed.
Once in the dungeon the scryers in her command centre warned her of bottlenecks and large opposing forces in the dungeon while at the same time coordinating the other attacking groups. Mercury used this time to calculate the enemy Keepers location which was transmitted to Jadeite who in turn teleported and attacked the Keeper directly, forcing hir to rapidly possess different minions and not to focus on the ongoing attack. This gave her the time to disconnect the dungeon heart from the rest of dungeon, voiding the claim on the land. At the same time her troops ferried the enemy's minions out of the portal or killed them, removing any other hosts for the Keeper.
The enemy Keeper's attempt in fleeing was thwarted by a collaborative pursuit of Mercury and Jadeite, with the result being the other Keeper's death by a telekinetically moved boulder.
As soon as the dungeon heart went inert, Mercury implemented her plan to move the heart to the sea and transport it to the Avatar Isles.
For this means she excavated a tunnel to a point a bit off-coast below the ocean. There her ice golems had already built a cone-shaped cave which Mercury partly filled with ice. Once the cave and tunnel were connected the inert heart was moved into the cave and the rest of the cave filled, too. Then the ceiling of the cave was widened to let the giant ice-block rise to the surface. With the proto-icebergs bobbing movements decreasing Mercury bonded with the heart, reactivating it.
After adding sufficient ice to ensure her plan, Mercury added a crude implementation of a screw and electric engine, running with coils and low-powered lightning traps to move the iceberg to the Avatar Islands.
On its way it ran afoul the Mukrezarian Blockade. One of its ships sent the rainbow fairies for reconnaissance, and the seven attacked. After single-handedly defeating and imprisoning the sisters, she sabotaged the ship and crossed the blockade.