Stymphalian Storm
One-Shot · 6 Players · Level 10 · 3–3.5 hrs · Lake-Clearing Hunt · Boss: Storm Matriarch
📜 Session Summary
| Style Heroic lake-clearing hunt with noisy tools, risky improvisation, and a final airborne brawl. |
| Win Condition The flock breaks, the lake reopens, and the last bronze feathers are claimed before they seed a wider plague. |
| Loss Condition The birds scatter into farms and roads; the lake survives, but every nearby roof and field becomes a target. |
| Players 6 × Level 10 · 3–3.5 hrs · 3 encounters |
| Key Ally Itys of the Whistling Reeds (recruit Enc. 1 or Enc. 2) · Maguffin: Thunder-Net of Stymphalos |
| Setting Lake Stymphalos — gray, shallow, reed-choked; the kind of lake that smells like rotting bronze and wet feathers; the village docks are half-collapsed from bird impacts; the rookery island is reachable only by skiff across open water under a flock-darkened sky. |
| Atmosphere Practical heroism with an edge of dark comedy — the birds are absurd and lethal simultaneously; the villagers have tried every obvious solution and been punished for it; the party must be clever in a situation where clever means "noisier than thunder, faster than a dive-bomb, and better at knots than the original net-makers." |
| Materials Tarred hemp net threaded with blue wire, bronze pinfeathers scattered like thrown knives on the dock boards, the smell of storm-charge and bird-musk, skiff-planks still vibrating from the last dive, Alkippe's note pinned under a lake reeve's knife. |
| Tone Kinetic and escalating — Enc. 1 is controlled chaos (evacuation under fire), Enc. 2 is creative problem-solving under duress, Enc. 3 is elemental and loud; the preferred end is flock-breaking not wholesale slaughter — Alkippe wants a lake she can fish again, not a trophy. |
Description
Alkippe Reed-Warden hooks the party with a problem and a confession in the same breath: the lake has been taken by bronze-beaked birds for two weeks, three fishing families are eating through their winter stores, and her brother looted an Ares-consecrated bronze piece from the shoreline that drew the flock back after it was supposed to have moved on. She has the Thunder-Net of Stymphalos — a single-use hunting net her grandmother's grandmother kept "for when the birds got ambitious." She doesn't know how to use it. She's hoping the party does.
The Stymphalian flock is not mindlessly dangerous — it's territorial. The bronze feathers they shed are structural, not ornamental: each one can punch through a skiff hull or pierce a leather vest. The Storm Matriarch who commands the rookery island at the lake's center is an ancient nesting-ground guardian of Ares, and she will not be dislodged by anything short of a decisive challenge at her own roost. The first two encounters are about surviving long enough and being clever enough to reach that island with the Thunder-Net intact.
The session is a three-beat escalation: clear the village docks (Enc. 1), herd the flock toward the rookery while crossing the lake (Enc. 2), then fight the Matriarch on her island with the net as the key payoff (Enc. 3). Handout DM payoff: when the Thunder-Net finally goes across the nest spire and the Matriarch drops to the rock, read the handout inscription. Let the players sit with the image of a storm-charged net catching something that should not be catchable.
Major Beats & DM Notes
- Opening — The Reed-Warden's Note. Alkippe pins her note beneath a lake reeve's knife because she assumes no one reads something just left on a table. The DM reads it aloud in full. A bronze feather is already embedded three inches into the dock boards near the party's feet — not as a threat, just as the ambient state of this lake. History DC 14: Stymphalian birds are Ares-consecrated; disturbing their roosting site requires either defeating the matriarch or honoring the dedication.
- Enc. 1 hook — Alkippe's Secret. Her brother Nikos looted a bronze piece. She won't say this immediately — Insight DC 14 on her face when she explains why the birds came back. Persuasion DC 15 or discovering the bronze cache yourself: she admits it, calls Nikos in, and the party can use the bronze as bait (grants Advantage on one Enc. 2 herding check). This also sets up her hard rule: she will not allow the party to poison the lake or torch nesting reeds.
- Enc. 2 hook — Bad Ideas Work. The DC 16 group challenge rewards creative thinking explicitly. If a player proposes something genuinely absurd (tied shields as wind-catchers, a bard performing a discordant thunder-imitation, a druid using Call Lightning to fake a storm front), award advantage on that success. Itys knows the reed-maze shortcut and can add a success for free if recruited.
- Enc. 3 RP hook — The Matriarch's Eggs. The Storm Matriarch has three egg mounds on the rookery island. Destroying them clears minion add-ons but worsens Alkippe's politics — the village has been selling Stymphalian feather-tips as arrowheads for years, and the birds haven't forgotten. Investigation DC 15 to recognize the egg mounds as guarded, not random. A PC who deliberately avoids the egg mounds earns the Matriarch's tactical hesitation (she won't use Lightning Screech against that PC).
- Thunder-Net payoff. The net strung across the nest spire during actual thunder (natural or summoned): Matriarch is Grounded 2 rounds and loses her reaction. The bells that remain after the net burns out become the reward. Let the net's handout echo when it deploys.
Session Rewards
Keepable prizes earned by completing (or excelling at) this session. One character claims each reward unless noted. Full cards are under Reward Cards.
| Reward | Description | Criteria |
|---|---|---|
| Thunder-Bell Cord of Stymphalos | Blue-wire bell cord that grounds a flyer and strips a reaction. | Clear the bronze-beaked flock; the spent thunder-net leaves singing bells behind. |
Creature / Enemy List
| Creature | Easy | Med | Hard | Notes |
|---|---|---|---|---|
| Bronze-Beaked Stymphalian | — | med | hard | CR 3 · Fast skirmisher |
| Razor-Feather Flock | — | med | hard | CR 5 · Area denial swarm |
| Nest Sentinel of Ares | — | med | hard | CR 6 · Armored bruiser |
| Storm Matriarch | — | med | hard | CR 9 · Boss, aerial controller |
| Itys of the Whistling Reeds | — | 1 | 1 | Recruit Enc. Enc. 1 or Enc. 2 |
Encounter 1 — Reeds Under Siege
Overview
Bronze-beaked birds are harassing the docks in rotating dives — not a full assault, but enough that no one can work the boats. The party must evacuate the exposed fishers, learn why the flock returned this season (Alkippe's brother and the stolen bronze), and choose their approach to the lake crossing ahead: bait-and-lure, thunder-distraction, or stealth through the reed-maze. Every choice they make here sets up the difficulty of Enc. 2.
APL 10 context: This is a skill encounter with combat pressure. Bronze-Beaked Stymphalians (CR 3 each) are dangerous in pairs — their flyby means they never take opportunity attacks. For Hard pressure, have 3–4 birds harry the docks while the party manages the evacuation.
🗺 Terrain
Flooded village docks · reed huts · half-sunk skiffs · bell tower (DC 12 climb, 30 ft. high, rings audibly on a hit) · bronze scratches on every surface below 10 ft.
Non-Combat Options
- Group Challenge (Primary Path). 4-success DC 15 group challenge using Nature (bird behavior), Survival (evacuation route), Athletics (skiff recovery), Persuasion (fishers won't move), or Animal Handling (calm panicked draft animal). Failure costs a skiff, a net cache, or 10 HP split among exposed villagers.
- Find the Bronze Cache. Investigation DC 14 in the dock shed or Insight DC 14 on Alkippe's face → discover Nikos's looted Ares-bronze. Returning it to the shore (Nature DC 13 to identify the right spot) grants Advantage on one Enc. 2 lure or bait check.
- Recruit Itys. He's trying to save his skiff from a dive-bomb. Athletics DC 12 to help him recover the skiff, or accept his reed-maze shortcut over Alkippe's objection. Either recruits him (joins Enc. 2 and 3).
Mechanics
- Combat pressure: 3–4 Bronze-Beaked Stymphalians harry the docks. They don't engage in sustained combat — they dive, deal damage, and disengage (flyby). Use them to apply time pressure on the evacuation challenge, not as a primary combat encounter.
- Win: 4 successes before 3 failures in the group challenge. The fishers are evacuated, the dock is clear, and the party has their approach strategy. Short rest opportunity if Nikos's bronze is returned and the birds settle.
Creature Cards
Alkippe Reed-Warden
Human lake reeve, exhausted civic hunter · Athletics +4 · Survival +5
Has managed this lake for 12 years; never dealt with an Ares-bird problem before
Motivation. Reopen the lake before hunger and panic make the townsfolk burn the marsh — she has 3 days before the village elder overrules her and authorizes fire.
Secret. Her brother Nikos looted Ares-bronze from a shoreline offering cairn and sold it as decorative scrap, not knowing what it would draw. She knows. Insight DC 14 reads her guilt when she explains why the flock returned. Persuasion DC 15 or finding the cache yourself: she tells the party directly and calls Nikos in to help as penance.
RP Hook. She respects clever solutions over violent ones. A party that proposes something genuinely creative for the lake crossing gets her approval — she'll use her reeve authority to source extra supplies for Enc. 2 (one extra lure raft, pre-positioned). Persuasion DC 13 to get her to commit once she hears the plan.
Hard rule. She will not allow the party to poison the lake, torch nesting reeds with families hiding nearby, or destroy more egg mounds than strictly necessary. She says: "I want a lake I can fish again. That means birds that leave, not birds that are dead."
Thunder-Net of Stymphalos
Storm-charged hunting net, single-use mythic snare
Appearance: A tarred hemp net threaded with blue wire and small bronze bells.
Handout. "Throw only when the sky answers. Pull only if you like keeping both arms."
Enc. 1–2. Can capture a scout bird, block a dangerous dive lane, or grant advantage on one flock-control check.
Enc. 3. If spread across the nest spire during thunder, grounds the boss for 2 rounds and strips its reaction.
Itys of the Whistling Reeds
Medium Humanoid, Neutral · Recruitable Ally · Local net-runner and bird-call mimic
AC 15 | HP 58 | Speed 30 ft.
Role: Local net-runner and bird-call mimic
RECRUITMENT (Enc. Enc. 1 or Enc. 2). Save his skiff, forgive his theft of bronze bait, or let him lead the reed-maze route.
Aid. Acts on party initiative when recruited; prefers nonlethal when asked.
Strike. Reed spear +6 to hit, 7 piercing; once per fight, mimic call imposes disadvantage on one bird dive.
Bronze-Beaked Stymphalian
Medium Creature · CR 3 · Fast skirmisher
AC 15 | HP 45 | Speed 30 ft.
Note. Use in pairs or as minion flights during dives.
Attack. Bronze beak +6 to hit, 10 piercing; flyby avoids opportunity attacks.
Encounter 2 — Thunder, Nets, and Bad Ideas
Overview
The party must cross the lake — open gray water with no cover — while managing aerial harassment and herding the flock toward the rookery before the birds scatter into the surrounding farmland and roads. Three lure rafts have been pre-positioned by the village; the party needs to activate them in sequence while surviving dive attacks. A lightning-struck standing stone at the lake's center marks the "herding threshold" — the birds will funnel toward the rookery if the party can drive them past it.
APL 10 context: This is a DC 16 group challenge (one step harder than Enc. 1) with Razor-Feather Flock (CR 5, 92 HP) attacks on failures. The challenge rewards creative improvisation explicitly — any genuinely inventive plan that could realistically produce thunder, light, or noise grants advantage on that success.
🗺 Terrain
Open gray water · 3 lure rafts (AC 11 / HP 15, each) · lightning-struck stone (center, waist-high, partial cover) · reed blinds at north shore (can hide 2 PCs each) · no solid ground between docks and rookery island.
Non-Combat Options
- Creative Thunder/Noise. Any spell or improvised approach that creates genuine loud thunder, dissonant sound, or blinding light (drums, tied shields as reflectors, a bard's thunderwave, Call Lightning from a druid, shouting into the standing stone's hollow base): automatic success on one challenge step. Itys's mimic call grants Advantage on one more step if he's recruited.
- Activate Lure Rafts in Sequence. Nature DC 14 to trigger each raft's scent-lure without alerting the birds prematurely. All 3 activated: the flock herds toward the rookery in one wave rather than two, reducing the number of failure triggers.
- Use the Thunder-Net Early. Spending the Thunder-Net here: capture a scout bird and use it as living bait — auto-success on one herding step and removes one Bronze-Beaked Stymphalian from Enc. 3's opening. Trade-off: the net's Enc. 3 boss payoff is lost.
Mechanics
- Challenge: 5 successes before 3 failures, DC 16. On a failure: a Razor-Feather Flock (CR 5) attacks for 2 rounds or destroys one prepared lure raft.
- Win: 5 successes. The flock herds toward the rookery; the party can land on the rookery island for Enc. 3. Short rest possible if the standing stone's natural shelter is used (DC 12 Survival).
Creature Cards
Thunder-Net of Stymphalos
Storm-charged hunting net, single-use mythic snare
Appearance: A tarred hemp net threaded with blue wire and small bronze bells.
Handout. "Throw only when the sky answers. Pull only if you like keeping both arms."
Enc. 1–2. Can capture a scout bird, block a dangerous dive lane, or grant advantage on one flock-control check.
Enc. 3. If spread across the nest spire during thunder, grounds the boss for 2 rounds and strips its reaction.
Itys of the Whistling Reeds
Medium Humanoid, Neutral · Recruitable Ally · Local net-runner and bird-call mimic
AC 15 | HP 58 | Speed 30 ft.
Role: Local net-runner and bird-call mimic
RECRUITMENT (Enc. Enc. 1 or Enc. 2). Save his skiff, forgive his theft of bronze bait, or let him lead the reed-maze route.
Aid. Acts on party initiative when recruited; prefers nonlethal when asked.
Strike. Reed spear +6 to hit, 7 piercing; once per fight, mimic call imposes disadvantage on one bird dive.
Razor-Feather Flock
Medium Creature · CR 5 · Area denial swarm
AC 14 | HP 92 | Speed 30 ft.
Note. Disperses for 1 round if hit by thunder damage.
Attack. Feather storm, DC 15 Dexterity save or 21 slashing in a 20-foot burst.
Nest Sentinel of Ares
Medium Creature · CR 6 · Armored bruiser
AC 17 | HP 110 | Speed 30 ft.
Note. Guards eggs and stolen bronze rather than fighting to the death.
Attack. Two talon strikes +7 to hit, 12 slashing each; shriek frightens on DC 15 Wisdom.
Encounter 3 — The Bronze Rookery
Overview
The rookery island is bone-white limestone barely above the waterline, dominated by a thorny nest spire 20 ft. high. The Storm Matriarch has been circling since the party set foot on the island — she knew they were coming. She isn't surprised; she is deciding. Two Nest Sentinels guard the egg mounds and 4 Bronze-Beaked Stymphalians make up her honor guard.
The Matriarch's storm crown is real — she can call actual lightning within the encounter's storm-cloud context, and the wind shifts she causes are structural (initiative 20 pulse). The Thunder-Net, if brought intact, is the only way to ground her without spending the entire party's resources: 2 rounds of no flight, no reaction, and vulnerability to the party's best burst window.
APL 10 Deadly check: Storm Matriarch (CR 9, 168 HP, LR 2/day equivalent in legendary resistances) + 2 Nest Sentinels (CR 6 each, 110 HP) + 4 Bronze-Beaks (CR 3 each, 45 HP). Effective XP with multipliers: ~Deadly for 6×L10. Don't reduce unless the party is severely depleted after Enc. 2.
🗺 Terrain
Bone-white island · thorny nest spire 20 ft. (difficult terrain to climb, DC 14) · waist-high water 10 ft. from shore (difficult terrain, drowning risk if unconscious) · three egg mounds (AC 11 / HP 20 each; destroying one ends 1 Bronze-Beak add but worsens political outcome) · storm clouds overhead (natural lightning possible at DM's call).
Non-Combat Options
- Thunder-Net Payoff. One action to spread the Thunder-Net across the nest spire (must be at spire base, net in hand) during a thunder moment (natural or summoned). Success: Matriarch is Grounded 2 rounds (speed 0, no flight, no reaction, vulnerable to damage types that aren't bludgeoning). Read the handout inscription when it deploys.
- Break the Flock Without Slaughter. When the Matriarch drops below 35 HP, Intimidation DC 16 or Animal Handling DC 16 (Advantage if Itys uses his mimic call simultaneously): the Matriarch retreats to the spire and the flock disperses. Alkippe's preferred outcome — she can work with birds that leave, not birds that are dead.
- Respect the Egg Mounds. A PC who visibly avoids the egg mounds and does not attack them: the Matriarch targets that PC last each round (her natural threat assessment treats deliberate non-aggression toward eggs as reduced priority). No check required — just play it as a declared intent each round.
Mechanics
- Wind Shift (Init 20): DC 15 Str or Dex save or slide 10 ft. toward water or nest spire spikes. Creatures in waist-high water: DC 12 Athletics to stand up as a bonus action.
- Lightning Screech (Recharge 5–6): 36 lightning/thunder in a 20-ft. cone. Creatures with total cover from spire or egg mound have Advantage on the save.
- Win: Matriarch reduced to 0 HP or driven off (≤35 HP + successful check). Surviving Nest Sentinels and Bronze-Beaks stand down when she retreats. The lake is clear.
Creature Cards
Thunder-Net of Stymphalos
Storm-charged hunting net, single-use mythic snare
Appearance: A tarred hemp net threaded with blue wire and small bronze bells.
Handout. "Throw only when the sky answers. Pull only if you like keeping both arms."
Enc. 1–2. Can capture a scout bird, block a dangerous dive lane, or grant advantage on one flock-control check.
Enc. 3. If spread across the nest spire during thunder, grounds the boss for 2 rounds and strips its reaction.
Bronze-Beaked Stymphalian
Medium Creature · CR 3 · Fast skirmisher
AC 15 | HP 45 | Speed 30 ft.
Note. Use in pairs or as minion flights during dives.
Attack. Bronze beak +6 to hit, 10 piercing; flyby avoids opportunity attacks.
Nest Sentinel of Ares
Medium Creature · CR 6 · Armored bruiser
AC 17 | HP 110 | Speed 30 ft.
Note. Guards eggs and stolen bronze rather than fighting to the death.
Attack. Two talon strikes +7 to hit, 12 slashing each; shriek frightens on DC 15 Wisdom.
Storm Matriarch
Large Creature · CR 9 · Boss, aerial controller · Boss
AC 18 | HP 168 | Speed 40 ft.
Role: Boss, aerial controller
Note. Boss last. Bloodied at half HP, she tries to lift the whole nest into the storm.
Hard encounter focus. Win condition may be steal, escape, disable, or drive-off — not always kill.
Multiattack / Assault. Multiattack with beak and two wings; lightning screech recharges on 5-6 for 36 lightning/thunder.
Advance (1). Move up to half Speed.
Strike (1). One attack from Assault.
⚖️ Difficulty Scaling
As Written ★ — 6 Players, Average Level 10
- Baseline for this guide. Encounter 1–2 are Hard; the final encounter is Deadly for six PCs at average level 10.
- XP budgets (6×L10 thresholds): Hard ≈ 10,800 · Deadly ≈ 16,800. Prefer adding elite pressure, legendary actions, or terrain danger over bloating minion counts past the choke.
Library Standard — 6 Players, Average Level 8
- Dial back: reduce boss HP ~20–25%; cut one legendary action option or recharge breath to 6 only; Favor/track thresholds −1 where present; skill DCs −1; drop one minion wave or −2 CR1–2 creatures from Hard openers.
Easier
- APL 8–9: use the Library Standard (6×L8) box, then shave one more minion wave or remove one recharge ability.
Harder
- APL 11–12: boss HP +20%; +1 legendary; final encounter gains one extra elite or lair pulse; skill DCs +1.
📋 Appendix — Cards
Alkippe Reed-Warden
Human lake reeve, exhausted civic hunter · Athletics +4 · Survival +5
Has managed this lake for 12 years; never dealt with an Ares-bird problem before
Motivation. Reopen the lake before hunger and panic make the townsfolk burn the marsh — she has 3 days before the village elder overrules her and authorizes fire.
Secret. Her brother Nikos looted Ares-bronze from a shoreline offering cairn and sold it as decorative scrap, not knowing what it would draw. She knows. Insight DC 14 reads her guilt when she explains why the flock returned. Persuasion DC 15 or finding the cache yourself: she tells the party directly and calls Nikos in to help as penance.
RP Hook. She respects clever solutions over violent ones. A party that proposes something genuinely creative for the lake crossing gets her approval — she'll use her reeve authority to source extra supplies for Enc. 2 (one extra lure raft, pre-positioned). Persuasion DC 13 to get her to commit once she hears the plan.
Hard rule. She will not allow the party to poison the lake, torch nesting reeds with families hiding nearby, or destroy more egg mounds than strictly necessary. She says: "I want a lake I can fish again. That means birds that leave, not birds that are dead."
Thunder-Net of Stymphalos
Storm-charged hunting net, single-use mythic snare
Appearance: A tarred hemp net threaded with blue wire and small bronze bells.
Handout. "Throw only when the sky answers. Pull only if you like keeping both arms."
Enc. 1–2. Can capture a scout bird, block a dangerous dive lane, or grant advantage on one flock-control check.
Enc. 3. If spread across the nest spire during thunder, grounds the boss for 2 rounds and strips its reaction.
Itys of the Whistling Reeds
Medium Humanoid, Neutral · Recruitable Ally · Local net-runner and bird-call mimic
AC 15 | HP 58 | Speed 30 ft.
Role: Local net-runner and bird-call mimic
RECRUITMENT (Enc. Enc. 1 or Enc. 2). Save his skiff, forgive his theft of bronze bait, or let him lead the reed-maze route.
Aid. Acts on party initiative when recruited; prefers nonlethal when asked.
Strike. Reed spear +6 to hit, 7 piercing; once per fight, mimic call imposes disadvantage on one bird dive.
Bronze-Beaked Stymphalian
Medium Creature · CR 3 · Fast skirmisher
AC 15 | HP 45 | Speed 30 ft.
Note. Use in pairs or as minion flights during dives.
Attack. Bronze beak +6 to hit, 10 piercing; flyby avoids opportunity attacks.
Razor-Feather Flock
Medium Creature · CR 5 · Area denial swarm
AC 14 | HP 92 | Speed 30 ft.
Note. Disperses for 1 round if hit by thunder damage.
Attack. Feather storm, DC 15 Dexterity save or 21 slashing in a 20-foot burst.
Nest Sentinel of Ares
Medium Creature · CR 6 · Armored bruiser
AC 17 | HP 110 | Speed 30 ft.
Note. Guards eggs and stolen bronze rather than fighting to the death.
Attack. Two talon strikes +7 to hit, 12 slashing each; shriek frightens on DC 15 Wisdom.
Storm Matriarch
Large Creature · CR 9 · Boss, aerial controller · Boss
AC 18 | HP 168 | Speed 40 ft.
Role: Boss, aerial controller
Note. Boss last. Bloodied at half HP, she tries to lift the whole nest into the storm.
Hard encounter focus. Win condition may be steal, escape, disable, or drive-off — not always kill.
Multiattack / Assault. Multiattack with beak and two wings; lightning screech recharges on 5-6 for 36 lightning/thunder.
Advance (1). Move up to half Speed.
Strike (1). One attack from Assault.
Reward Cards
Post-session keepables. Reward is the first tag. Mechanics below are for ongoing use after this oneshot.
Thunder-Bell Cord of Stymphalos
Reward · Wondrous · 1/Long Rest
Mechanics. Once per long rest, as an action, you cast the cord like a net (range 15 feet, one Medium or smaller flying creature). On a hit (ranged attack), the target is restrained until the end of your next turn, falls if it relies on wings, and can't take reactions while restrained this way. While carried, once per short rest you can impose disadvantage on one creature's next ranged attack made within 30 feet of you (reaction, when you hear or see the attack declared).
Appearance. A tarred hemp cord threaded with blue wire and three small bronze storm-bells.
Lore. Residue of the Thunder-Net after Stymphalos's sky answered and the nest was grounded.
Quote. "Throw only when the sky answers. Pull only if you like keeping both arms." — Thunder-Net
Earn when: Clear the bronze-beaked flock; the spent thunder-net leaves singing bells behind.