The water feels frigid yet pulsates with an unseen rhythm as adventurers wade through the cave, its luminescent algae illuminating the path. Jagged coral lines the cavern walls, adorned with eerie bioluminescent markings that exude an unsettling tranquility as they glimmer in sync with the dim tides. Each step sends a ripple through the tranquil surface, and beneath lurk shifting shadows that whisper secrets of the deep—a telltale sign of the trap soon to unleash chaos. Suddenly, as the water swells ominously, a colossal wave crashes, the abyss of bludgeoning force smashes down with violent ferocity, while tendrils of coral erupt, constricting the unwary, ensnaring adventurers in a watery grave.

Gameplay Notes: The Drowning Caverns Trap

Trap Activation

• Triggering the Trap: The trap activates when at least one character steps on a pressure plate hidden in the shallow waters of the cavern. This can happen while moving through the designated area (usually a corridor or a rounded chamber adjacent to the deeper waters).
• Environment Conditions: The trap can only be activated when the water level reaches a specific height (determined by the DM – for instance, half the player height). High tides will reduce visibility and awareness, complicating player movements.

Detection and Disarm Notes

• Detection Checks:

  • Perception (DC 15): Players might feel a sudden change in temperature in the water as it begins to chill or warm, revealing something is amiss.
  • Investigation (DC 16): Looking closely at the water, players can notice unusual currents that hint at the underwater mechanisms.
  • Arcane Insight (DC 18 with Arcana): Detecting faint magical energy from sigils on the walls will alert the players to the potential for a magical trap.

• Disarm Mechanism:

  • Arcana Check (DC 20): To deactivate the sigils and lessen the tidal wave’s impact. Success means they temporarily reduce the damage by half for the next wave.
  • Investigation Check (DC 18): Identifying the sequence of pressure plates to effectively disable them. Players can take an action to attempt this each round. A failure results in triggering the trap again within the same round.

Suggested Tactics and Variations

• Adjusting Difficulty:

  • NPC Assistance: Consider throwing in the assistance of local aquatic allies or enemies who can offer help or insight regarding the trap.
  • Varying Water Levels: As the trap progresses, have the water level change drastically (maximum height causing disadvantage to players or conditions like being unable to swim).

• Targeted Attacks: The trap could focus its effects on weaker characters who are more susceptible to being restrained or submerged, using currents to grab them.

Initiative and Round Actions

• Initiative: The trap has a base initiative of +2. Roll initiative at the start of the activation round.
• Actions Per Round (3 Rounds total):

  1. First Wave (Round 1):

     • Attack Roll: +8 to hit against all players in the area.
     • Effect: Inflicts 8d10 bludgeoning damage and triggers the drowning hazard (DC 15 Strength save).

  2. Coral Ensnarement (Round 2):

     • Attack Roll: Same as before against players (who are still affected by the first wave).
     • Effect: Players who failed the previous round’s check face additional effects from coral tendrils. Each player must make a DC 16 Dexterity saving throw; failure leads to being restrained (escape by Strength (Athletics) DC 18).

  3. Tidal Vortex (Round 3):

     • Environmental Change: The water swells to its highest level. Players must make Dexterity saving throws (DC 14) or be forced to the nearest walls—given susceptibility to temporary flooding, this might lead to becoming incapacitated if conditions are severe enough.
     • Dynamic Hazard: Introduces a chaotic current, affecting initiative rolls or causing players to swap positions randomly without consent.

Round-by-Round Effects

• Phase 1: Round 1

  • The players trigger the tidal wave, suffering initial damage with a chance to become submerged.

• Phase 2: Rounds 2-4

  • Players experience increasing pressure from water and coral tendrils emerge.
  • The sensation of being restrained or dominated by water serves as a notable constraint.

• Phase 3: Round 5 Onward

  • If the trap remains active, players have only one more chance to escape, facing maximum burst damage or drowning based on their physical conditions.
  • By now, traps begin to make chaotic efforts to displace characters, leading to profound tension and increased urgency in resolving the situation.

Additional Tips for Running the Trap

• Visual and Audio Cues: Engage players with descriptions of the water’s movement, sounds of bubbling currents, and glowing marine life, increasing tension.
• Player Communication: Encourage players to think creatively to interact with the environment—using magic, items, or environment around them.
• Pacing the Actions: Ensure prompt rounds, allowing each player engagement when it’s their turn, and speeding through the trap elements so as not to linger too long and distract from the immersion.
• Keep a Tidal Tracker: Maintain a visual aide with water levels, ongoing effects, and character statuses (submerged, restrained) to easily update players.

With this structured approach, the Dungeon Master will be prepared for a flowing and dynamic experience, ensuring the Drowning Caverns becomes a memorable moment in their campaign!