Tartarus

A burning, cursed dimension under the world, with its own biomes, the river Phlegethon, and things locked down there for a reason.

Getting there

Craft an Altar of Tartarus and give it a Nether Star. It burns green for good, and touching it takes you down. You keep your x and z and land on the ground, or on a small brick landing if there is none, with a lit altar next to you to get back.

Dangers

Tartarus Fire gives Wither, Weakness, Slowness and Damnation.
The Phlegethon burns, gives Damnation II and takes 3% of max health twice a second.
Weeping Asphodel and Watcher Lily blind you when you walk through them.

Biomes

Biome	What's there
Ashen Thicket	A dense wood of dead trees, thorn shrubs and ash grass.
Phlegethon Mire	Magma and the river's banks, thick with Weeping Asphodel. River shrines are more common here.
Spire Fields	Dense fields of spikes and thorn shrubs. Kapelos' camps can show up here.
Tartarus Wastes	The default ground of the pit: spikes, dead trees, magma and fire. Kapelos' camps can show up here.

Structures

Structure	What it is
Hades' Ruins	Scattered over every Tartarus biome, in four variants: a broken colonnade temple with a bronze Hades on his throne, a titan's cell, a sunken judgement court and a small shrine on the Phlegethon bank. Each has a loot chest and a lit altar to get home.
Kapelos' Camp	A flat round of brick and sand with a stall under a striped awning, soul lanterns and a green fire. Kapelos the Shade-Peddler is tied to the spot. Found in the Tartarus Wastes and Spire Fields.
Thanatos Arena	A raised dais with the Altar of the Last Breath in a sunken fighting floor, three rows of seats up to a rim of broken pillars and hooded mourners, and four gates over the ramps down, one of them collapsed. This is where the boss fight is started.

The Last Breath

The boss fight of the mod, with its own music and a red sky.

Hunt the pit for the trophies and craft an Obol of the Last Breath.
Find a Thanatos Arena and set the coin on the Altar of the Last Breath. The coin rises, spins and bursts.
Phase one: The Veiled Mourner comes out of the floor.
Kill it and the shroud comes off. Phase two: Thanatos, the Last Breath.

Only one fight per area. The boss stays in its arena: past the edge it is pulled back. Bring light or holy damage, and spiritual attacks.