Aquatic Adventures III: Rules

The heavy weighted net refused to loose its grip on Kyvid. Its death-grip, he now realized. He had sunk so deep it had now gone completely black. He struggled again, wriggling and writhing is desperation as he continued to sink deeper and deeper. Even with his charm of water breathing he was struggling for breath, the water felt like a weight blanket pressing down upon him from all sides. His ears ached and his eyes feel tight in their sockets. He would not survive this depth for long.

This is the third in a series of blogs on Aquatic Adventures. This article provides some needed rules for underwater combat.

Layered Combat

One of the solutions for 3D combat proposed last time was layered encounters: multiple battlemaps each focusing on a single slice of the action.

Layers are an abstraction on standard combat, ignoring precise movement and distance in favour of a simple system that is easy to run. Instead of tracking elevation for each creature, there are multiple maps all stacked vertically. This is similar to having a combat take place in several small rooms, all adjacent to each other.

Despite being separate maps, layers are still treated as the same map or location for rituals and powers that target the entire battlefield. Creatures are able to see and hear across all layers unless blocked by additional terrain.

For ease of movement between layers, it’s a good idea to number the grid for identification, like as a chessboard – or the game Battleship.

As a default, layers are treated as being approximately five squares apart.

Moving Between Layers

• Creatures must move to adjacent layers.
• A moving creature appears in a square at the same position as the one they left or a square adjacent to that one.
• Creatures with a swim speed can move between adjacent layers as a move action. They do not need to make an Athletics check to change layers.
• Creatures without a swim speed need two move actions to move between layers. They must make an Athletic check to change layers.
• Creatures cannot end their turn between layers.
• Creatures provoke Opportunity Attacks normally for leaving threatened squares.
• Forced movement that moves a creature more than five squares can instead be used to move a creature between layers. The forced movement must still obey other limits (i.e. you cannot pull a creature on the same layer onto a different layer).
• Creatures that fail three Athletics checks in a row by 5 or more sink to a lower layer.

Attacking Between Layers

• Attacking between layers does not impose a penalty on attack rolls.
• Melee and close attacks cannot target creatures on a different layer.
• Ranged and area attacks with a range of 5 or less cannot target a different layer.
• Ranged and area attacks with a range of 6 to 10 can target an adjacent layer.
• Ranged and area attacks with a range of 11 to 15 can target up to two layers away.
• Each subsequent range increase of 5 can target an additional layer.

Skills

The skills chapter of the PHB and Rules Compendium includes all the DCs for moving in water, including treading water. This section adds a few more options for skill use.

Athletics

Skilled swimmers can attempt more while underwater than the frail or unskilled.

• Immobilized creatures can still make Athletics check to avoid sinking; they cannot move but can still tread water.
• A creature that does not move or make an Athletics check sinks 1 square at the end of its turn.
• If a creature succeeds on an Athletics check to swim by 10 or more, it does not need to spend an extra square of movement for the first square it enters.

Endurance

Only the hardy can withstand the crushing pressure of the deep sea.

Action: A free action made at the start of a creature’s turn

DC: The DC is based on the type or pressure. DC 15 for light pressure and DC 22 for heavy pressure.

Success: A creature can ignore the effects of deep sea pressure for the encounter.

Pressure

Water is heavy, and without magic the pressures of being deep underwater can crush an unprepared diver.

There are two types of pressure: light pressure and heavy pressure. In the open sea, light pressure is between 100 feet and 500 feet underwater (20 squares to 100 squares), while heavy pressure is 500 feet or more underwater (over 100 squares).

• In areas of light pressure, creatures without the aquatic keyword take a -2 penalty to Perception checks and all Dexterity-based skill checks.
• Light pressure can be ignored for an encounter with a DC 15 Endurance check.
• In areas of heavy pressure, creatures without the aquatic keyword take a -5 penalty to Perception checks and all Dexterity-based skill checks.
• Heavy pressure can be ignored for an encounter with a DC 22 Endurance check.
• Effects and abilities that permit breathing underwater do not bestow the ability to ignore pressure.
• Effects and abilities that remove penalties for underwater combat bestow the ability to ignore pressure.
• Creatures without the aquatic keyword that move from a depth with no pressure to heavy pressure (or the reverse)  in less than one minute, take damage equal to their bloodied value and are deafened (save ends).

Falling & Sinking

In many ways, sinking is falling, only slower and with no damage.

• Creatures sink 1 square at the end of their turn.
• If a creature fails an Athletics check to swim by 5 or more they sink.
• Immobilized creatures must still make Athletics checks to swim or they sink. Failure or success does not end the immobilized condition.
• Grabbed creatures do not sink unless the grabbing creature chooses. They can still choose to make Athletics checks to tread water.
• Grabbing creatures can either chose to sink with a grabbed target, make a single Athletics check to tread water for itself and the target, or use the target’s Athletics check.
• Restrained creatures do not sink, unless the DM rules the individual power does not prevent sinking. This does not end the restraining condition.

Next Time

On the next blog in this series I will provide a couple sample layers and additional terrain to use in underwater adventures.

Similar Posts:

•      Aquatic Adventures II: Encounters
•      Aquatic Adventures I: Introduction & Advice
•      4e and the Art of the Limit-Break: Divine Limit Breaks