Tartarus is not just a plane of existence like the Celestial Kingdom or the Feywild; it is a living, breathing entity. This god-like being encapsulates a plane of flesh within its body, serving as the only tunnel back to the mortal realm from Pandemonium, the kingdom of Hades. Some say that earthquakes in the mortal plane occur when Tartarus stirs from its slumber. The anatomy of consists of long tunnels and canals, resembling veins and vessels that lie empty of blood, while pockets of dark, acidic green fluid occasionally boil and erupt, searing the flesh of the muscular walls they land on. Tartarus never ceases to grow, create, and birth new horrors. The dimension within its body is a temple to its form, an arena for its creations, and a tomb for its offspring.
Monsters, born from the flesh walls of Tartarus, are driven solely by the instinct to survive. These "Children of Tartarus" constantly battle each other and any intruders, ensuring that only the strongest survive for more than a day. Among these children, three have achieved legendary status for their endurance and strength: the Mother, the Father, and the Hound. The Mother and Father however escaped Tartarus years ago and the Hound is still trapped in the arena of its creation.
The entrance to Tartarus from Pandemonium is a pulsating, fleshy portal. Passing through requires a DC 18 Wisdom saving throw to resist the overwhelming sense of dread. Failure results in the frightened condition for 1 hour.
Acidic Geysers: Pockets of dark green acid erupt randomly. Each creature in a 10-foot radius must make a DC 16 Dexterity saving throw, taking 4d6 acid damage on a failure, or half as much on a success.
Pulsating Walls: The flesh walls periodically contract, making movement difficult. Every hour spent in Tartarus, creatures must make a DC 15 Constitution saving throw or gain one level of exhaustion.
HP: 130 (17d10+34)
AC: 15 (natural armor)
Speed: 40 ft. (+10 for flight)
Saves: Dex +5, Con +6, Wis +3
Traits:
Multiattack (2–3 attacks depending on form)
Regenerate 1d4 of HP each round unless damaged by fire or radiant
Actions: Bite, Claw, (vary by form)
Reactions: When first bloodied, it can Disengage or Dash as a reaction.
Roll a 1-2: Nothings spawn but the walls twitch, something almost arrived
Roll a 3+: The walls shake and you know your no longer alone
Roll a 1: Lone predator
Roll a 2: Hunting pair
Roll a 3: Triad pack
Roll a 4: Brood swarm of 1d6
Roll a 1: Winged (can fly and swoop)
Roll a 2: Emits a deafening shriek (Con Save or be deafened 1 min).
Roll a 3: Gains one extra attack per round when bloodied.
Roll a 4: When falls to half HP, splits into two bodies with a shared HP
Roll a 5: Vortex-like maw, (Dex Save or grappled inside).
Roll a 6: Paralyzing hiss (DC 12 Wis save or skip next action)
Roll a 7: Dies after a critical hit, exploding in a 10-ft acid spray (Dex save DC 13, 2d6 acid).
Roll a 8: Spews sticky white foam. Foam clings like webs: 10-ft radius counts as difficult terrain.
Roll a 9: Can fuse itself to the ground, gain +2 AC and resistance to bludgeoning, but can't move next round.
Roll a 10: If reduced to 0 HP, it twitches and reforms in 1d4 rounds unless burned.
The Hound is a massive, three-headed lupine beast, exuding an aura of primal terror and raw power. Each head, distinctly different in its menacing characteristics. The Hound's body is a horrifying amalgamation of powerful muscles and sharp, protruding bones, covered in matted, bloodstained fur. The sinewy muscles ripple beneath its skin, never settling even when the beast is standing still. Each head's attempt to dominate the others, they snap at each other, trying to assert control.
This central head is the largest and most ferocious, with fangs as long as daggers that can tear flesh from bone with terrifying ease. Its eyes burn with a hellish red glow, and its breath is a constant cloud of steam, reeking of decay and blood. The fur around its mouth is perpetually stained dark with the blood of its victims, and its jaws snap shut with bone-crushing force.
Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 4d10+6 piercing damage plus 2d10 acid damage.
The devourer of the minds and left head has eyes that shimmer with an eerie, almost hypnotic light. Its gaze seems to pierce into the soul, unravelling thoughts and memories. The head is slightly smaller but no less deadly, with an elongated snout and jagged teeth that drip with a viscous, greenish saliva.
Psychic Attack: Targets one creature it can see within 30 feet. The target must make a DC 18 Wisdom saving throw or take 4d10 psychic damage and lose one random memory of player and/ or DMs choice.
the devourer of souls, has a more spectral appearance. Its fur is darker, almost shadow-like, and its eyes are deep voids that seem to draw in light and hope. When it breathes, a chilling, ethereal mist escapes its nostrils, whispering the anguished cries of the souls it has consumed. This head's mouth opens unnaturally wide, revealing a dark abyss that seems to pulse with a life of its own.
Soul Consumption: Targets one creature it can see within 10 feet. The target must make a DC 18 Charisma saving throw or have its soul devoured. On a failure, the target takes 6d10 necrotic damage and has disadvantage on death saving throws for 1d8 days.
Multiattack: The Hound makes three bite attacks, one with each head.
Heads of Discord: Each head can act independently, allowing the Hound to make one additional action per head that is not incapacitated.
Guardian of the Heart: While within 60 feet of the Heart of Tartarus, the Hound gains resistance to all damage types and advantage on all saving throws.
Temple of Flesh: The centre of Tartarus contains a temple-like structure made of bone and sinew. Here, a powerful artefact known as the "Heart of Tartarus" must be destroyed to open a portal back to the mortal realm.
Heart of Tartarus: AC 20, HP 150, immune to psychic and poison damage, resistant to all other damage types. Destroying it requires a DC 20 Strength (Athletics) check to hit and deal damage.