To reflect the harshness of life on Athas, a long rest doesn't heal all your damage. instead you must use your Hit dice to heal damage. 

Sleeping will restore half of your maximum Hit dice.

Resting during the day must be done with shelter. Without shelter no rest can occur, short or long.

At the end of the day (night), determine how much food and water was consumed, utilizing the DMG's foraging rules (p111). Characters moving at a normal slow pace may attempt to forage by making a Wisdom (survival) check: DC 10 for abundant food and water sources, DC 15 for limited, and DC 20 for very little. Those who succeed find 1d6 + Wisdom modifier pounds of food  or gallons of water.
*A character can forage for food or water, but not both. All foragers must declare before they roll.
*Only characters proficient in survival can forage.

Use the table below to determine food and water need for characters. Water needs are doubled if the DM explains that the weather is hot for at least 1 hour of the travel day (40+degrees Celsius). Water needs are halved if travelling at night.

Size Food per Day Water per Day

Small 1 pound 1 gallon

Medium 1 pounds 1 gallon

Large 4 pounds 4 gallons

We will be using physical representations on the table to visualize this.

Each day without food will be tracked as "days without food." Eating half the daily food requirement counts as half a day without food (round down so that every two days on half-rations counts as one full day).

A character can go 3 + their Constitution modifier in days without food before they begins to starve. At the end of each day beyond that limit, they suffer one level of exhaustion.

Each day a starving character eats their full daily requirement for food, they reduce their days without food count by two. Until the days without food count is back to zero, they will have at least one level of exhaustion that cannot be removed by any means except eating.

At the end of each day, a character who did not consume the daily requirement of water gains one level of exhaustion, or two levels if the character has one or more levels of exhaustion from any source already.

A character who drinks only half the water amount can make a DC 15 Constitution save to avoid exhaustion.

The extreme heat rules will almost always apply every day in Athas (DMG p110). Characters exposed to the heat and without access to water must make a Constitution saving throw at the end of each hour of exposure (DC 5 + 1 per hour after the first) or gain a level of exhaustion.

Those wearing Medium or Heavy armors have disadvantage on this save.

Anyone foolish enough to wear metal armor in extreme heat also requires double their normal allotment of water.

Remember, a long rest can remove one level of exhaustion, but the character must consume at least half rations and half water for this to occur.

Your Strength score determines the amount of weight you can bear. The following terms define what you can lift or carry.

Carrying Capacity.

Your carrying capacity is your Strength score multiplied by 10. This is the weight (in pounds) that you can carry.

Push, Drag, or Lift.

You can push, drag, or lift a weight in pounds up to twice your carrying capacity (or 20 times your Strength score). While pushing or dragging weight in excess of your carrying capacity, your speed drops to 5 feet.

Size and Strength.

Larger creatures can bear more weight, whereas Tiny creatures can carry less. For each size category above Medium, double the creature’s carrying capacity and the amount it can push, drag, or lift. For a Tiny creature, halve these weights.

If you carry weight in excess of 2 times your Strength score, you are encumbered, which means your speed drops by 10 feet. If you carry weight in excess of 3 times your Strength score, up to your maximum carrying capacity, you are instead heavily encumbered, which means your speed drops by 20 feet and you have disadvantage on ability checks, attack rolls, and saving throws that use Strength, Dexterity, or Constitution. 

The same rules for size in carrying and lifting apply.

Anytime a death save is required the DM will roll behind screen and keep record.

If you have at least 10' reach with a weapon or by size, you may use your Action to attack with your reach property weapon if someone without at least 10' reach enters your threatened area, you are aware of them, and you are currently wielding the weapon, even if your initiative count is worse. This does not allow you to take more than one turn but instead reflects the initial advantage a longer weapon has in keeping enemies at bay, and it can be waived. Once a foe is within your threatened area, this cannot be applied unless they were to leave and return. If you have multiple attacks then you may use the remainder of your attacks on your initiative turn.

Your critical hits, no matter what your rolls, will do at least the maximum damage to the base weapon. For example, a d8 longsword will do at least 8 damage before other modifiers are added in. A 4d8 monster bite will do at least 32 damage. Any other variables are not affected.

When making a melee attack, creatures can receive a + to hit depending on the number of creatures flanking. As long as at least two allies are on opposite sides of an enemy, within 5 feet of the enemy, then each ally will receive +1 to hit per ally in range. A maximum of +5 can be achieved.

Nonmetal weapons are prone to breaking. Once per turn, if you do maximum damage on a weapon die (e.g. 8 on a 1d8) or roll a natural 1 on the attack, the weapon breaks on a 1 or 2 on a second d20 roll. This does not apply to weapons that fire ammunition such as bows. However, non-metal ammunition is not recoverable.

Once per turn means that no matter how many attacks you take on your turn, only one breakage roll is. made. However, if you make and attack of opportunity as a reaction, it counts as another turn and breakage rules would apply again.

Against metal armors, non-metal weapons automatically break instead of checking the d20.

For 150cp, a weapon can be improved with one unique masterwork feature. Weapons cannot be improved more than once.

• Accurate. Reduces AC granted by cover by 1 to ammunition weapons.

• Aerodynamic. Ammunition weapon range increased by +10/40 and thrown by +5/15.

• Alternate damage. Add bludgeoning, piercing, or slashing quality to a weapon.

• Deadly. Reroll (once) all 1s on a damage roll. This cannot be used if another feature allowed a reroll.

• Defensive. As reaction to a melee attack, add +1 to AC. If dual-wielding, add +2. Does not function with a shield.

• Disarming. Gain +1 to disarm attacks, +2 if using weapon 2-handed (DMG 271).

• Fine. Double weapon's hardness (if any), hit points, and reduce break chance (if any) by 5% (by 1 on d20).

• High Critical. Any 1s rolled for critical damage are treated as 2s.

• Tripping. Gain +1 to shove, +2 if using weapon 2-handed.

For 150cp, light or medium armor can be improved with one unique masterwork feature. Heavy armor costs 300cp. Armor cannot be improved more than once. Shields can only apply the "lightweight" property.

• Absorbent. Resistance to poison damage against weapons with Poison.

• Efficient. Requires half the time to don or doff.

• Enclosed. Resistance to damage from splashed materials and contact poisons.

• Lightweight. Reduces weight by 4 pounds for light or medium armor. For medium armor, removes (if any), stealth disadvantage. Heavy armor has weight reduced by 10 and removes Strength requirement. Shields have weight reduced by half and remove Strength requirement (if any).

• Quick-escape. Removing this armor only requires an action. Donning it is unaffected.

• Reinforced. Immune to deadly or high critical hit properties from the optional weapon rules.

For realism, in order for armor to fit a creature it was not intended for, an expert in crafting must apply her craft to resize armor up to one size category larger or smaller, at a cost of 1d4 x 10 (or 10% to 40%) of the market price of the item.

Spell Level

Create or Destroy Water 1st

Continual Flame 2nd

Create Food and Water 3rd

Water Walk* 3rd

Control Water 4th

Conjure Woodland Beings 4th

Conjure Fey 6th

Conjure Celestial** 7th

Tsunami*** 8th

All planar travel spells

*Renamed "Silt Walk" and only works on silt.

**Planar spells only impact elemental beings as celestials and fiends do not exist in Dark Sun.

***This is renamed "Sand Storm" and uses sand, not water.

The rarity of metals has led casters to find substitutes. If a spell calls for a metallic component, such as 50 gp (cp) worth of powdered iron, it is assumed a substitute is permissible, such as 50 cp worth of powdered jade.

For flavor and role play purposes only, any spell that purports to have a metallic effect (e.g. blade barrier) thematically can have it replaced with obsidian, bone, etc. Similarly, spells that require a watery component (e.g. Simulacrum, snow) are replaced with an Athas equivalent (e.g. sand or silt).

• If used with a bonus action to take or give, you make the appropriate roll.

• If used with an action to take or give, gain the maximum possible roll.

• You may sheath one weapon and unsheathe another as a single free object interaction.

• one player rolls from the players' side (using any initiative adjustments from any player), DM rolls for monsters.

• Higher roll picks one member to go first and turns alternate from side to side until everyone has had a turn. 

• Sides can determine the order as they go and can change from round to round. 

• When one side has completed all their turns the remaining side completes all remaining turns in any order they choose.

• Players, and enemies may now make grapple attacks when making an attack of opportunity.

Exhaustion [Condition]

While you have the Exhaustion condition, you experience the following effects.

Exhaustion Levels. This condition is cumulative. Each time you receive it, you gain 1 Exhaustion level. You die if your Exhaustion level is 6.

D20 Tests Affected. When you make a D20 Test, the roll is reduced by 2 times your Exhaustion level.

Speed Reduced. Your Speed is reduced by a number of feet equal to 5 times your Exhaustion level.

Removing Exhaustion Levels. Finishing a Long Rest removes 1 of your Exhaustion levels. When your Exhaustion level reaches 0, the condition ends.