Deep Skeleton Dragon

What — A titanic undead dragon at the bottom of a ~220-ft pit below a burned dormitory in the deep Menagoles Mines (Session 52). Far larger than any dragon the party has met — the GM's own frame is "full Elden Ring boss fight, bring all your friends level of enemy." Its natural, root-hung chasm connects to the mine's overflow water pipe (anything sucked into the filter-pipe would surface here), and it is one of three candidate culprits for the pile of bodies in its lair: the humanoids killed it, it killed the humanoids, or a gas killed both.

Threat — Boss-tier, and now fully assessed: killed in Session 54. Roughly 700 hit points, AC needing a 15, damage reductions across the board with piercing reduced hardest (the archers reverse-engineered it at a third to a half), and a refusal-to-die mechanic on top. It went down in five rounds to a level-7 party of six. The GM afterwards: "I thought that dragon was going to be way worse than it was."

Observed traits (Session 52)

• Legless / serpentine. Has no legs; rises like a snake, lifting its body on its back muscles; rock and debris spill from its ribcage as it moves; its head cracks the cave ceiling on rising — it is big.
• Blind, scent-hunting. No eyes and a poor Perception (+4); when disturbed it takes the Search action (DC 10 to notice a small intruder) and then scents for a creature "that has passed through recently," walking in the target's general direction without truly locating them.
• Slow to rouse. Reacts to being stood on by getting up and hunting confusedly, not by instantly chasing — a small, quiet creature can slip away.

Tactics & behavior — Dormant at the pit's bottom until physically disturbed. On waking it searches by sound and smell rather than sight; a scent-only lock means stealth and distance beat it. It made no attempt to climb the narrow (~5–7 ft) pit after Lash.

Disposition to the party — Hostile if engaged, but too blind and slow to have pinned Lash; left behind alive when the party barricaded the pit with a door.

Session 53 — scouted in its lair, and how it died the first time

• Reached from the far side. Lash's barrel blast opened the old cave-in into a back route: a stair of 15–20 ft ledges, deep water, then a flooded stomach-crawl the dragon cannot fit through — so the approach doubles as a guaranteed escape. The party crossed it on Pass Without Trace with a worst roll of 19.
• It sleeps again. After ~6–10 hours it had settled back to rest; it never woke during the visit. The GM's standing rule: it rouses to being stood on, not to quiet company.
• The lair, seen properly. A flooded "water domain skeletal death room" — a huge pool, weeds and thicket, a broken overflow pipe venting into it, and the floor carpeted in bones and whatever else the mine's filters have swept down here. (That bone litter is the ammunition for the Bonestorm it uses in Session 54.) It is a dead end: the only other way out is a narrow wiggle space above and behind it, the hole Lash originally fell through, and the pipe, which climbs away steeply.
• Its ears are not its nose. The check to notice Fenric at the sword was a flat Perception, explicitly not a scent roll — its scent-tracking and its ordinary senses are separate, and the ordinary ones are bad. It rolled a 6.
• Something killed it once. A +2 dragon-slaying short sword is driven up through the soft of its lower jaw and out the middle of its forehead — the original killing blow, still embedded. From the angle, the GM reckons a bite would have taken the wielder's arm and half their torso in the same moment: likely an exchange of killing blows, which is why nobody ever came back for the sword.
• Identified without waking it. Fenric hooked one claw-tip round the grip (Sleight of Hand 16, advantage plus one of Lash's dice, against the dragon's Perception 6) and used his Spellbreaker instant Identify. The sword is fully embedded — unretrievable while the thing animates.
• Rated. The GM: killing it would take "a couple hours next week" and is "possibly doable for a mid-level adventuring group with some preparation." Worth a pip — possibly a pip and a half.

Session 54 — killed, and what it could actually do

The party came back through the flooded crawl on Pass Without Trace and killed it in about five rounds. It slept through the entire approach again, including a 20-ft crawl and six characters taking position around it. Its full kit, finally seen:

• Two actions a turn, and it spent both on the biggest thing available. It also has a claw attack it cannot use, having no arms, and a passive suite that mostly makes it immune to being moved or knocked over — it is a worm; it has nothing to knock over.
• Control costs it whole turns. Thalia's Entangle caught it asleep (Strength save at disadvantage, rolled 14, failed) and it was restrained for a full round while the party attacked with advantage. Breaking out took both its actions — one failed check at 16, then a 17. It has no legendary resistance and nothing that shrugged off the condition.
• Faster than the party on the ground. Lash's History check (17) on its earlier pursuit (Session 52) establishes it was gaining on her as she ran — it can chase down a fleeing character over open floor, and only the narrow crawl it cannot fit through ever made it escapable.
• Breath weapon — rears halfway between a snake and a worm and breathes a cone of black sinew, acid and dark magic wide enough to catch five characters. The target chooses the save: Dexterity for all-or-nothing (make it and you slip the cone entirely), or Constitution to weather it, taking 32 necrotic minus whatever you rolled. It counts as magical, which gave Fenric advantage. Recharges.
• Consume into the Ribcage (both actions) — the ribs click open one at a time, it scoops a character up, and interlocks them like fingers to blend the victim into viscera. DC 18 Strength; failure means being swallowed and taking roughly 86. Silithane made it on a –1 modifier by burning Heroic Inspiration, shoved one rib aside and fell out of the hole as it snapped shut — 24 piercing instead.
• Bonestorm (the GM's own file calls it "Bonenado") — it noodles almost vertical and gyrates, and every bone buried in the chamber tears free and spins counter-clockwise through the room. One Dexterity save against cumulative thresholds: under 30, 4 bludgeoning; under 25, 13 more; under 20, prone and 18 more; under 15, restrained under bone rubble; under 10, heavy damage; under 5, lifted into the cyclone and slammed into a wall; under 0, death outright — the GM has literally written the word. Everyone on the map was under both of the first two thresholds, so the whole party took 17; Fenric and Lash were also under 20 and took 35, which dropped Lash. The GM's later reckoning rounds it to "like 40 damage to people" — each, not shared.
• Tail attack — 17 to 27 bludgeoning, aimed at whatever is behind it. The 27 knocked Silithane unconscious.
• Bite — 18 piercing; it took one at Salamandine late in the fight.
• Target selection. With no eyes it still fought smart: it turned the cone to catch five at once, went for the character it could swallow, then hunted the prone and the downed — turning on Fenric while he was flat for advantage, and crawling across the room for Jex on the high ledge rather than staying with the melee.
• Refusal to die. At 0 hit points it makes an escalating Constitution save each time it would drop: DC 5 (cannot fail), DC 10 (cannot fail), DC 15, DC 20. Magra's crit through the spinal column felt like the kill and wasn't; Jex then double-critted a creature already at 1 hit point purely to burn its saves. What finally killed it was the Booming Blade already sheathing it triggering when it crawled toward Jex — cast by Silithane, who was unconscious on the floor by then, the GM ruling after some deliberation that the boom persists without its caster. DC 20, failed.

How it died the first time, confirmed. Two magic weapons and nothing else survived the centuries in the body: the +2 short sword through the jaw and forehead, and a +3 arrow lodged where the heart would be, shot through the ribs from the far side. There were at least two of them, and they were equipped for this.

The loot. Magra freed the sword by pulling the skull off it (Athletics 16) after Silithane failed outright; Silithane pulled the arrow out of the spine and into himself for doubled damage, because he is a dragon, and it went to Jex on a coin-flip. Up to 70 teeth were salvageable in principle and all of them too waterlogged to use. The black ichor it breathed still burns anyone who touches it. The bones were left where they fell, mostly in the water. Party reached level 8.

Status — Dead. Woken at Session 52, scouted at Session 53, killed at Session 54 — the party's first slain draconic creature, on the GM's own reckoning "maybe the second rung on the ladder": no arms, no legs, no wings, and already dead when they got to it.

SUMMARY: The boss-sized blind legless undead dragon of the deep Menagoles Mines — ~700 HP, a necrotic breath cone, a rib-cage swallow and a bone cyclone, plus escalating saves to refuse death — killed in five rounds in Session 54, giving up a +2 dragon-slaying short sword and a +3 dragon-slaying arrow and taking the party to level 8.