4E Planes of Law Mechanics

The 4E Manual of the Planes covers a fair share of the planes from the Great Wheel cosmos, albeit with some modifications. I’ll try my hand at mechanics for the missing planes as well as missing features of the included planes, using an “original Planescape cosmos with 4E rules” approach. Note that these are just rough drafts with some mechanics only loosely defined - hazards and skill challenges are suggested but not presented in detail.

The first set suggests mechanics for the lawful planes: Baator, Acheron, Mechanus, Arcadia, and Celestia. Inspiration comes from the original 2E Planes of Law product. I’ll eventually try to cover the entire Great Wheel and feedback would be greatly appreciated.

Celestia

As is (4E MotP p91), though with original layer-structure and environment.

Radiance Affinity: Attacks with the radiance keyword gain a +1 bonus to the attack roll, and attacks with the necrotic keyword deal half damage (ongoing necrotic damage is not affected). This trait is directly from 4E MotP.

Reward of the Just: The nature of the plane makes helping others more worthwhile. Cooperation on skill checks (PHB p179) and the Aid Another action (PHB p287) gives a +3 bonus rather than +2.

The Silver Sea: Upon entering the plane travelers arrive falling in the holy sea of Lunia – their swim to shore is the first test of diligence, a fundamental virtue of Celestia. The traveler makes a single Athletics check to represent the entire swim against DC 15 at heroic tier, 20 at paragon, and 25 at epic (the plane presents greater challenges to those of greater power). Failure summons a zoveri to aid the traveler ashore, though if he’s trained in Athletics he suffers a -1 penalty to Diplomacy checks with the natives for his entire stay in Celestia. The holy waters are damaging to evil immortals (I assume here that we change demon and yugoloth origin from elemental to immortal, as the 4E MotP suggests for the Great Wheel).

Paths of the Virtuous: Progressing up the mountain-side to access higher layers is most efficient by adhering to Celestia’s virtues and philosophical paths. The DM might call for a Skill Challenge for the PCs to successfully reach the next layer, using Insight, Endurance, and Religion as primary skills with higher complexity for higher layers. Complexity 1 to ascend from the 1st Heaven, complexity 2 to ascend from the 2nd Heaven, and so on. Ascending from the 6th layer and into the top Heaven of Chronias cannot be accomplished this way, naturally.

Arcadia

Gravity: Normal

Mutability: Divinely mutable (deities control their own environs).

Geometrical Perfection: When three or more creatures are arranged next to each other in a straight line, they all receive +1 to attacks and any forced movement effects against them can be prevented with an immediate saving throw. These benefits are lost if the line is broken or another creature moves adjacent without extending the straight line.

Arcadian Consistency: Once per day, upon using an attack power, any creature can add the Reliable keyword to the power as a Free Action.

Strict Hierarchy: Charisma-based skill checks receive a +1 bonus when interacting with a character of lower level and take a -1 penalty when interacting with a character of higher level.

Mechanus

Gravity: Towards nearest cog side. Stepping over the edge of a cog allows reorientation to gravity on the opposite side.

Mutability: Normal. Even deities within their own realms have limited power if the changes they attempt violate the fundamental laws of Mechanus. The cogs turn endlessly and no known power can stop them.

Everything As It Seems: Bluff checks take a -2 penalty and powers with the illusion keyword take a -1 penalty to attacks.

Gears of Mechanus: The cogs of Mechanus are all interconnected and always turning. Serious injury can result from crossing carelessly or being forced over the edge near the crossing point to or from a small cog (DM’s discretion). Treat as a paragon tier obstacle hazard when such incidents occur, targeting Reflex, using high limited damage values (DMG p42), and causing the target to be restrained (save ends).

Habitable Atmosphere: Any creature with a respiratory system can breathe Mechanus’ air, even if they normally only can breathe underwater.

Perfect Comprehension: Within Mechanus all speech turns into one language that is perfectly understood by everyone in the plane.

Acheron

Gravity: Towards nearest iron cube face. Stepping over the edge of a cube allows reorientation to gravity on the adjoining side.

Mutability: Divinely mutable (deities control their own environs). Cubes also move of their own accord, though usually too slowly to have any game mechanical effect.

Cube Collision: Occasionally, Acheron iron cubes drift into collision course with each other. When the PCs are caught off-guard near the impact zone of such an event, the DM might treat the collision as a Skill Challenge using Acrobatics, Athletics, and Perception as primary skills with failed checks resulting in damage and loss of healing surges (suitable for overland escape from larger cube collisions), or as a blaster hazard with close burst attacks vs Reflex that gradually increase in burst area (suitable for smaller cube collisions where the PCs cannot readily escape or are engaged in combat).

The River Styx: The River Styx flows through Avalas and might present an epic tier obstacle hazard if the PCs are engaged in combat nearby or otherwise stressed (targeting Will and eventually resulting in total amnesia).*

Ringing Resonance of Tintibulus: Tintibulus features iron polygonal blocks in addition to cubes and these blocks constantly collide with each other. The collisions create a constant ringing sensation that imparts a -5 penalty on Perception checks.

Razor Shards of Ocanthus: Ocanthus features no blocks but only razor thin plates of black ice. The larger ones support weight readily, but the smaller ones effectively become deadly cutting shards. These can present frequent paragon or epic tier blaster hazard to the unsheltered, targeting Reflex, using low normal damage values (DMG p42) and dealing ongoing damage.

Baator

As is (4E MotP p97), though with original layer-structure and environment, and without the Plummet to Avernus trait.

Cold Affinity (Stygia and Cania only): Attacks with the cold keyword gain a +1 bonus to the attack roll, and attacks with the fire keyword deal half damage (ongoing fire damage is not affected). This trait is directly from 4E MotP.

Corruption (Minauros and Maladomini only): Attacks with the disease or poison keyword gain a +1 bonus to the attack roll. Healing powers restore only half as many hit points as normal. This trait is directly from 4E MotP.

Fire Affinity (Avernus, Dis, Phlegethos, and Nessus only): Attacks with the fire keyword gain a +1 bonus to the attack roll, and attacks with the cold keyword deal half damage (ongoing cold damage is not affected). This trait is directly from 4E MotP.

Fireballs of Avernus: Balls of fire rain down from Avernus’ sky and seem drawn towards areas of strife and conflict. These might be treated as blaster hazards of heroic and paragon tier that target Reflex, deal low limited fire damage in a close burst (DMG p42), and possibly also ongoing fire damage (save ends).

The River Styx: The River Styx flows through Avernus, Stygia, and Nessus, and might present an epic tier obstacle hazard if the PCs are engaged in combat nearby or otherwise stressed (targeting Will and eventually resulting in total amnesia).*

*: More detailed ideas for the Styx:

Attack vs Will.

Hit: The target forgets the events of the encounter and loses the use of its highest level unused daily power as if it has been expended; 2nd consecutive hit: the target also forgets the events of the day; 3rd consecutive hit: the target also suffers total amnesia (only special epic rituals can restore memory).

Miss: The target forgets the events of the last round.

Hit or Miss: If the target was sustaining any powers, it seizes to do so. The target takes a -2 penalty to skill checks until it takes an extended rest.