Mother of the Deep Coil
One-Shot · 6 Players · Level 12 · ~3–3.5 Hours · 2 Encounters · Echidna Lair (Phase 3 Deadly)
📜 Session Summary
| Style Lair Assault — Outer Brood skirmish → Multi-phase Echidna (Phase 3 Deadly) |
| Win Condition Defeat Echidna (0 HP) in her nest at Arima |
| Players 6 × Level 12 · Duration 3–3.5 hrs · Structure 2 encounters (Enc. 2 is long) |
| Override Final phase is Deadly (user request). No Typhon. No Cerberus among summons. |
| Maguffin Tripod Brand of Arima · QG: Melitta of Delphi |
Description
Mist opens on the Cilician foothills above the deep of Arima — where the Mother of Monsters coils in her own darkness. Clear the outer brood, descend the chimney, and endure three rising phases as Echidna calls her children. Press the brand when she calls a name you cannot afford.
Lair Setting — Arima
- Locale: Cilicia — cave mouth in a ravine → bone-chimney → gargantuan nest-cavern with black pool.
- Maps: Enc. 1 ravine ledge 60×40; Enc. 2 nest 100×80 with 20×20 pool, bone shelves, 40-ft ceiling.
- Summon ban: Echidna may call many children — not Typhon, not Cerberus. Orthrus (two-headed) is fine.
- Rest: Short Rest only between Enc. 1 and 2 (the nest wakes). No Long Rest inside.
Major Beats
- Melitta + Tripod Brand at the mist-line.
- Enc. 1: Outer Brood — death dogs, harpies, dracaena; recruit Kimon.
- Enc. 2: Multi-phase Echidna — Phase 1 Hard → Phase 2 Bard-Hard → Phase 3 Deadly.
- Victory: Mother slain / nest stills; brood scatters into myth.
Creature / Enemy List
| Creature | Easy | Med | Hard | Notes |
|---|---|---|---|---|
| Death Dog | 2 | 3 | 4 | Enc. 1 / summons |
| Brood Harpy | 2 | 3 | 4 | Enc. 1 |
| Dracaena Guard | 1 | 2 | 2 | Enc. 1 |
| Orthrus | — | 1 | 1 | Phase 2 summon |
| Chimera | — | 0–1 | 1 | Phase 2–3 |
| Brood-Hydra | — | — | 1 | Phase 3 |
| Echidna | adj | 1 | 1 | Boss |
Encounter 1 — The Outer Brood
Overview
Bone-littered ravine before the chimney. 3× Death Dogs + 2× Brood Harpies + 1× Dracaena Guard. Kimon is pinned under a collapsed goat-pen (½ cover).
🗺 Terrain
60×40 ravine · chimney entrance north (climb Ath DC 12 down 40 ft. after fight) · scree difficult terrain in two 10-ft patches.
Mechanics
- Non-combat path: Offer meat/wine + Animal Handling/Persuasion group 3 successes before 3 failures (DC 14) to draw dogs off while the party slips to the chimney — still face 1 dracaena at the lip (or bribe her with treasure 50+ gp).
- RECRUITMENT: Free/heal Kimon → Enc. 2 Guide / Warning Cry.
- Brand: disadv on one brood-beast’s attacks vs. brand-wielder (1/SR).
- Rest: Short Rest only at chimney mouth; something huge exhales below.
Creature Cards
Death Dog (Two-Headed Brood)
Medium Monstrosity, Neutral Evil · CR 1 · Mini-optional
AC 12 | HP 39 | Speed 40 ft.
Two heads: adv on Perception · Sleep / charm: save once for both heads
Not Cerberus. Two-headed only — never stage as Cerberus.
Multiattack. Two bites.
Bite. +4 to hit. Hit: 5 (1d6+2) piercing + Con DC 12 or poisoned; fail by 5+ also diseased (HP max −3 until cured).
Brood Harpy
Medium Monstrosity, Chaotic Evil · CR 1
AC 11 | HP 38 | Speed 20 ft., fly 40 ft.
Nest scouts of the outer chimney
Claws. +3 to hit. Hit: 6 (2d4+1) slashing.
Luring Song. 300 ft.; Wis DC 11 or charmed + incapacitated, move toward harpy. Ends if damaged / deafened.
Dracaena Guard
Large Monstrosity, Neutral Evil · CR 3 · Echidna’s door-wardens
AC 14 | HP 68 | Speed 30 ft.
Woman-serpent hybrids; speak broken Common
RECRUITMENT (optional). If reduced without a killing blow and offered mercy (Persuasion DC 15), one may hiss a warning about Phase 2’s Orthrus — then flees. Not a combat ally.
Multiattack. Spear and constrict.
Spear. +5 to hit. Hit: 8 (1d8+3) piercing.
Constrict. +5 to hit. Hit: 10 (2d6+3) bludgeoning + grapple (escape DC 13).
Kimon the Goatherd-Scout
Medium Humanoid, Neutral Good · CR 1/2 · Recruitable
AC 12 | HP 18 | Speed 30 ft.
Lost his flock to the Outer Brood; knows a side-chimney into Enc. 2
RECRUITMENT. Spare him / heal him in Enc. 1 (Medicine DC 12 or any healing). In Enc. 2 he can Guide once: party ignores difficult terrain from bone-scree for 1 round, or points out a ½-cover ledge.
Sling. +4 to hit, range 30/120. Hit: 4 (1d4+2) bludgeoning.
Warning Cry. Bonus action: one ally within 30 ft. not surprised by a Call Brood arrival this round.
Tripod Brand of Arima
Wondrous Item (maguffin), Unique
Appearance: iron brand, ash-black, warm; Delphic laurel stamp
Handout (22 words). "When the Mother calls her children from the dark, press this ash-iron to the stone — the nest forgets one name."
Enc. 1. Action (1/short rest): brand a brood-beast within 5 ft. — it has disadvantage on attacks vs. you until end of its next turn.
Enc. 2 payoff. Action once per phase: press to nest stone / Echidna’s coil. Cancel her next Call Brood (or dismiss one summoned creature of CR 5 or less as it arrives). Phase 3: instead, for 1 round Echidna cannot use Call Brood and has disadvantage on Constrict.
Encounter 2 — Mother of the Deep Coil (Multi-Phase)
Overview
The nest opens: black pool, bone shelves, Echidna coiled half in water. She fights in three phases as HP falls. Budget this as the session’s main dish.
🗺 Terrain
100×80 cavern · central pool 20×20 (deep) · bone shelves (½ cover, climb DC 10) · two nest tunnels (summon entry points).
Phase Rules
Phase 1 — Coil and Call (HP 310–207) · Hard
- Echidna uses full Multiattack; Call Brood (R5–6): 2× Death Dogs or 1× Dracaena + 1× Harpy.
- Lair actions on; Legendary Actions: Detect / Tail / Hiss (no Phase-3 Call).
- Brand: cancel next Call Brood once this phase.
Phase 2 — Children of the Nest (HP 206–104) · Hard+
- On transition (first time she enters this band): immediate free Call Brood — summon Orthrus (preferred) or Brood Sphinx.
- Call Brood options expand: Orthrus, Chimera (if Orthrus already out, prefer 2 Death Dogs + Harpy), Dracaenae.
- Lair: Coil Quake unlocked. Venom Spew preferred vs. clustered casters.
- Brand: cancel one Call or dismiss one CR ≤5 summon on arrival (once this phase).
Phase 3 — Blood-Mother Ascendant (HP 103–0) · DEADLY
- Deadly by design. On transition: roar — each enemy Wis DC 16 or frightened until end of its next turn; then free Call Brood: Lernean Brood-Hydra or Chimera + Orthrus if Hydra too heavy for your table.
- Echidna gains +2 to hit; Bite poison DC 19; Call Brood legendary (cost 3) available.
- Max summons raised; Hydra counts as 2 toward cap.
- Brand finale: 1 round — no Call Brood + disadv on Constrict (once).
- Win: Echidna 0 HP. Remaining summons flee into tunnels (chase optional, not required).
DM Pacing Notes
- Keep summoned turns fast — telegraph attacks, use average damage if slow.
- If Phase 3 will TPK unfairly due to dice: have Hydra arrive with 3 heads instead of 5, or delay legendary Call once.
- Still no Typhon cameo. Still no Cerberus.
Creature Cards
Echidna, Mother of Monsters
Gargantuan Monstrosity, Chaotic Evil · CR 14 (phases escalate to Deadly) · BOSS
AC 17 (natural) | HP 310 (20d20+100) | Speed 40 ft., burrow 20 ft., swim 40 ft.
Saves: Dex +7, Con +10, Wis +8 · Resist: poison, BPS nonmagical · Immune: poisoned · Senses: darkvision 120 ft. · LR 3/day
Gargantuan Coil. Space 20×20 ft. (tail sweeps further). Occupies nest pool + shore. PCs can move through her space as difficult terrain (she may Constrict as OA once per turn).
Mother’s Call. See phase rules — she summons brood. Never Typhon. Never Cerberus. Prefer Orthrus, Chimera, lesser Hydra, Sphinx, Death Dogs, Harpies, Dracaenae.
Phase Thresholds. Phase 1: HP 310–207. Phase 2: 206–104. Phase 3 (Deadly): 103–0 — Blood-Mother Ascendant.
Persistence. Defeating her (0 HP) ends the threat of this awakening. She is a monster-mother, not a god — world remains intact. Typhon is absent (elsewhere / sealed); do not introduce him.
Multiattack. One Bite and one Constrict, or two Tail Sweeps.
Bite. +12 to hit, reach 15 ft. Hit: 20 (3d8+7) piercing + 14 (4d6) poison (Con DC 18 or poisoned 1 minute).
Constrict. +12 to hit, reach 10 ft. Hit: 21 (4d6+7) bludgeoning + grapple (escape DC 20). Until grapple ends, target is restrained; Echidna can’t constrict another.
Tail Sweep. +12 to hit, reach 20 ft. Hit: 16 (2d8+7) bludgeoning; Str DC 20 or prone.
Call Brood (Recharge 5–6). Summon brood per current phase (see encounter). Arrives in unoccupied spaces within 60 ft. Max summoned creatures at once: Phase 1 = 3, Phase 2 = 4, Phase 3 = 5 (Hydra counts as 2).
Venom Spew (Recharge 5–6). 30-ft cone Dex DC 18; 28 (8d6) poison; failure also blinded until end of next turn.
Drag Under. Move a constricted creature 15 ft. toward nest pool; if pool entered, creature is underwater (hold breath rules).
Detect (1). Wis (Perception) check.
Tail (1). One Tail Sweep.
Hiss (2). One creature within 60 ft. Wis DC 18 or frightened until end of its next turn.
Call (3, Phase 3 only). Use Call Brood even if not recharged; then Call Brood recharges on 6 only until she finishes a long rest.
Bone Scree. Difficult terrain in a 20-ft radius until next init 20.
Nest Gasp. Poison fog lightly obscures a 30-ft cube for 1 round; entering/starting there Con DC 15 or 7 (2d6) poison.
Coil Quake (Phase 2+). Each creature on ground within 30 ft. Dex DC 15 or prone.
Tripod Brand of Arima
Wondrous Item (maguffin), Unique
Appearance: iron brand, ash-black, warm; Delphic laurel stamp
Handout (22 words). "When the Mother calls her children from the dark, press this ash-iron to the stone — the nest forgets one name."
Enc. 1. Action (1/short rest): brand a brood-beast within 5 ft. — it has disadvantage on attacks vs. you until end of its next turn.
Enc. 2 payoff. Action once per phase: press to nest stone / Echidna’s coil. Cancel her next Call Brood (or dismiss one summoned creature of CR 5 or less as it arrives). Phase 3: instead, for 1 round Echidna cannot use Call Brood and has disadvantage on Constrict.
Orthrus
Large Monstrosity, Neutral Evil · CR 5 · Two-headed hound · NOT Cerberus
AC 14 | HP 85 | Speed 50 ft.
Brother of Cerberus in myth — do not replace with Cerberus. Two heads only.
Pack Howl. Allied brood within 30 ft. have advantage on melee attacks vs. a creature Orthrus has bitten this turn.
Multiattack. Two bites.
Bite. +7 to hit. Hit: 11 (2d6+4) piercing + Con DC 14 or poisoned 1 minute.
Double Maw (Recharge 5–6). One bite at +7 with advantage; Hit: 18 (4d6+4) piercing and knock prone.
Chimera
Large Monstrosity, Chaotic Evil · CR 6 · Classic brood-child
AC 14 | HP 114 | Speed 30 ft., fly 60 ft.
Lion / goat / dragon heads
Multiattack. Bite, horns, and claws.
Bite. +7. Hit: 11 (2d6+4) piercing.
Horns. +7. Hit: 10 (1d12+4) bludgeoning.
Claws. +7. Hit: 11 (2d6+4) slashing.
Fire Breath (Recharge 5–6). 15-ft cone Dex DC 15; 31 (7d8) fire.
Lernean Brood-Hydra (Lesser)
Huge Monstrosity, Unaligned · CR 8 · Staged lesser hydra · Phase 3 summon
AC 15 | HP 150 (heads matter more) | Speed 30 ft., swim 30 ft.
Starts with 5 heads. Not immortal regeneration — simplified for Deadly pace.
Multiple Heads. 5 heads. While it has >1 head, adv on saves vs. blind/deaf/stun/charm. Loses 30 HP → lose 1 head (and one bite from Multiattack). At 0 heads, dies.
Reactive Heads. 1 reaction per head for opportunity attacks.
Multiattack. As many bite attacks as it has heads (max 5).
Bite. +8 to hit, reach 10 ft. Hit: 10 (1d10+5) piercing.
Brood Sphinx (Winged Riddler)
Large Monstrosity, Lawful Evil · CR 5 · Optional Phase 2 alternate
AC 15 | HP 102 | Speed 40 ft., fly 60 ft.
Spell DC 14 — minor illusion, detect magic; Roar once
Multiattack. Two claws; may replace one with Roar if available.
Claw. +7. Hit: 11 (2d6+4) slashing.
Roar (1/day). Each creature of its choice within 60 ft. Wis DC 14 or frightened 1 minute.
⚖️ Difficulty Scaling
As Written ★ — 6 Players, Average Level 12
- Baseline for this guide. Numbers, DCs, and win tracks assume six PCs at average level 12.
Library Standard — 6 Players, Average Level 8
- Reduce boss HP ~30–35%, strip one phase or one legendary action; minion counts −30%; Phase/Deadly language becomes Hard if present.
Easier
- APL 10–11: use Library Standard, then remove the deadliest phase rider.
Harder
- APL 13–15: restore full mythic pressure — extra phase or spawn; DCs +2.
📋 Appendix — Cards
Quest / Item / Ally
Melitta of Delphi (Quest Giver)
Medium Humanoid, Neutral · Oracle’s courier
Mist → Cilician foothills; carries sealed pythia-ash
Motivation. Livestock, heroes, and whole patrols vanish into Arima’s deep. The Pythia names the Mother of Monsters awake in her own coil — she must be defeated in her lair before her brood spills into the plains.
Secret. Apollo will not enter the nest. Mortals must. The brand she gives was quenched in the Pythia’s tripod — it bites Echidna’s summons.
Override note. This session is 2 encounters; Enc. 2 is a long multi-phase fight. Phase 3 is Deadly by design (user override of the usual Hard-cap).
Tripod Brand of Arima
Wondrous Item (maguffin), Unique
Appearance: iron brand, ash-black, warm; Delphic laurel stamp
Handout (22 words). "When the Mother calls her children from the dark, press this ash-iron to the stone — the nest forgets one name."
Enc. 1. Action (1/short rest): brand a brood-beast within 5 ft. — it has disadvantage on attacks vs. you until end of its next turn.
Enc. 2 payoff. Action once per phase: press to nest stone / Echidna’s coil. Cancel her next Call Brood (or dismiss one summoned creature of CR 5 or less as it arrives). Phase 3: instead, for 1 round Echidna cannot use Call Brood and has disadvantage on Constrict.
Kimon the Goatherd-Scout
Medium Humanoid, Neutral Good · CR 1/2 · Recruitable
AC 12 | HP 18 | Speed 30 ft.
Lost his flock to the Outer Brood; knows a side-chimney into Enc. 2
RECRUITMENT. Spare him / heal him in Enc. 1 (Medicine DC 12 or any healing). In Enc. 2 he can Guide once: party ignores difficult terrain from bone-scree for 1 round, or points out a ½-cover ledge.
Sling. +4 to hit, range 30/120. Hit: 4 (1d4+2) bludgeoning.
Warning Cry. Bonus action: one ally within 30 ft. not surprised by a Call Brood arrival this round.
Boss
Echidna, Mother of Monsters
Gargantuan Monstrosity, Chaotic Evil · CR 14 (phases escalate to Deadly) · BOSS
AC 17 (natural) | HP 310 (20d20+100) | Speed 40 ft., burrow 20 ft., swim 40 ft.
Saves: Dex +7, Con +10, Wis +8 · Resist: poison, BPS nonmagical · Immune: poisoned · Senses: darkvision 120 ft. · LR 3/day
Gargantuan Coil. Space 20×20 ft. (tail sweeps further). Occupies nest pool + shore. PCs can move through her space as difficult terrain (she may Constrict as OA once per turn).
Mother’s Call. See phase rules — she summons brood. Never Typhon. Never Cerberus. Prefer Orthrus, Chimera, lesser Hydra, Sphinx, Death Dogs, Harpies, Dracaenae.
Phase Thresholds. Phase 1: HP 310–207. Phase 2: 206–104. Phase 3 (Deadly): 103–0 — Blood-Mother Ascendant.
Persistence. Defeating her (0 HP) ends the threat of this awakening. She is a monster-mother, not a god — world remains intact. Typhon is absent (elsewhere / sealed); do not introduce him.
Multiattack. One Bite and one Constrict, or two Tail Sweeps.
Bite. +12 to hit, reach 15 ft. Hit: 20 (3d8+7) piercing + 14 (4d6) poison (Con DC 18 or poisoned 1 minute).
Constrict. +12 to hit, reach 10 ft. Hit: 21 (4d6+7) bludgeoning + grapple (escape DC 20). Until grapple ends, target is restrained; Echidna can’t constrict another.
Tail Sweep. +12 to hit, reach 20 ft. Hit: 16 (2d8+7) bludgeoning; Str DC 20 or prone.
Call Brood (Recharge 5–6). Summon brood per current phase (see encounter). Arrives in unoccupied spaces within 60 ft. Max summoned creatures at once: Phase 1 = 3, Phase 2 = 4, Phase 3 = 5 (Hydra counts as 2).
Venom Spew (Recharge 5–6). 30-ft cone Dex DC 18; 28 (8d6) poison; failure also blinded until end of next turn.
Drag Under. Move a constricted creature 15 ft. toward nest pool; if pool entered, creature is underwater (hold breath rules).
Detect (1). Wis (Perception) check.
Tail (1). One Tail Sweep.
Hiss (2). One creature within 60 ft. Wis DC 18 or frightened until end of its next turn.
Call (3, Phase 3 only). Use Call Brood even if not recharged; then Call Brood recharges on 6 only until she finishes a long rest.
Bone Scree. Difficult terrain in a 20-ft radius until next init 20.
Nest Gasp. Poison fog lightly obscures a 30-ft cube for 1 round; entering/starting there Con DC 15 or 7 (2d6) poison.
Coil Quake (Phase 2+). Each creature on ground within 30 ft. Dex DC 15 or prone.
Outer Brood & Summons
Death Dog (Two-Headed Brood)
Medium Monstrosity, Neutral Evil · CR 1 · Mini-optional
AC 12 | HP 39 | Speed 40 ft.
Two heads: adv on Perception · Sleep / charm: save once for both heads
Not Cerberus. Two-headed only — never stage as Cerberus.
Multiattack. Two bites.
Bite. +4 to hit. Hit: 5 (1d6+2) piercing + Con DC 12 or poisoned; fail by 5+ also diseased (HP max −3 until cured).
Brood Harpy
Medium Monstrosity, Chaotic Evil · CR 1
AC 11 | HP 38 | Speed 20 ft., fly 40 ft.
Nest scouts of the outer chimney
Claws. +3 to hit. Hit: 6 (2d4+1) slashing.
Luring Song. 300 ft.; Wis DC 11 or charmed + incapacitated, move toward harpy. Ends if damaged / deafened.
Dracaena Guard
Large Monstrosity, Neutral Evil · CR 3 · Echidna’s door-wardens
AC 14 | HP 68 | Speed 30 ft.
Woman-serpent hybrids; speak broken Common
RECRUITMENT (optional). If reduced without a killing blow and offered mercy (Persuasion DC 15), one may hiss a warning about Phase 2’s Orthrus — then flees. Not a combat ally.
Multiattack. Spear and constrict.
Spear. +5 to hit. Hit: 8 (1d8+3) piercing.
Constrict. +5 to hit. Hit: 10 (2d6+3) bludgeoning + grapple (escape DC 13).
Orthrus
Large Monstrosity, Neutral Evil · CR 5 · Two-headed hound · NOT Cerberus
AC 14 | HP 85 | Speed 50 ft.
Brother of Cerberus in myth — do not replace with Cerberus. Two heads only.
Pack Howl. Allied brood within 30 ft. have advantage on melee attacks vs. a creature Orthrus has bitten this turn.
Multiattack. Two bites.
Bite. +7 to hit. Hit: 11 (2d6+4) piercing + Con DC 14 or poisoned 1 minute.
Double Maw (Recharge 5–6). One bite at +7 with advantage; Hit: 18 (4d6+4) piercing and knock prone.
Chimera
Large Monstrosity, Chaotic Evil · CR 6 · Classic brood-child
AC 14 | HP 114 | Speed 30 ft., fly 60 ft.
Lion / goat / dragon heads
Multiattack. Bite, horns, and claws.
Bite. +7. Hit: 11 (2d6+4) piercing.
Horns. +7. Hit: 10 (1d12+4) bludgeoning.
Claws. +7. Hit: 11 (2d6+4) slashing.
Fire Breath (Recharge 5–6). 15-ft cone Dex DC 15; 31 (7d8) fire.
Lernean Brood-Hydra (Lesser)
Huge Monstrosity, Unaligned · CR 8 · Staged lesser hydra · Phase 3 summon
AC 15 | HP 150 (heads matter more) | Speed 30 ft., swim 30 ft.
Starts with 5 heads. Not immortal regeneration — simplified for Deadly pace.
Multiple Heads. 5 heads. While it has >1 head, adv on saves vs. blind/deaf/stun/charm. Loses 30 HP → lose 1 head (and one bite from Multiattack). At 0 heads, dies.
Reactive Heads. 1 reaction per head for opportunity attacks.
Multiattack. As many bite attacks as it has heads (max 5).
Bite. +8 to hit, reach 10 ft. Hit: 10 (1d10+5) piercing.
Brood Sphinx (Winged Riddler)
Large Monstrosity, Lawful Evil · CR 5 · Optional Phase 2 alternate
AC 15 | HP 102 | Speed 40 ft., fly 60 ft.
Spell DC 14 — minor illusion, detect magic; Roar once
Multiattack. Two claws; may replace one with Roar if available.
Claw. +7. Hit: 11 (2d6+4) slashing.
Roar (1/day). Each creature of its choice within 60 ft. Wis DC 14 or frightened 1 minute.