Poisons and Diseases

Each time a Malady triggers its effects (including when it is first caught), the victim suffers the current Stage's effects and makes a Recovery Check against the Disease's DC. The victim can also make a Recovery Check whenever the they take a Meal or longer rest.
The Stage of the disease is determined by the Severity of the Malady, which is determined by the starting Stage of the malady, which is in turn determined by the victim's Save against it.
When the victim takes a Meal, they can expend a number of Hit Dice equal to their Strength Bonus to make a Recovery Check. When they take a Long Rest, they can expend any number of Hit Dice to attempt a Recovery Check.
When the Severity is reduced to 0, the malady is cured.

Recovery Checks

Roll the Malady's listed Save against its DC + Stage. If you fail, increase the Severity by the Danger. If you succeed, you automaticaly expend 1 Hit Die, roll it and reduce the Severity by Hit Die + Strength Bonus.

Resting and proper medical attention can assist with the recovery process. The two stack with each other.
When the victim completes a Night's Rest or Respite, they can immediately attempt a Recovery Check. If they succeed, then they can use a number of HD up to the Bonus from the afflicted Attribute (instead of just rolling one HD), or twice as many HD if it was a Respite.
A creature can also apply medical attention over the course of a Meal or longer rest. To do so, they must attempt a Medicine Check with DC of Malady DC + Stage.
If they succeed:

• Field Medicine (Meal): reduce the Severity by the medic's Wisdom Bonus. This Check can only be made once per Malady.
• Basic Treatment (Night's Rest or Respite): when the victim makes their next Recovery Check, they add the medic's Wisdom Bonus to the Check.
• Full Treatment (Respite): in addition to the effects of Basic Treatment, when the victim would increase the Severity it increases by half as much, and when they would decrease the Severity it decreases by twice as much.

After Full or Basic Treatment, the medic gains 1 Exhaustion Level.
Multiple creatures can work together to treat the victim during a Night's Rest or Respite. If they do, each must make the Medicine Check (though an expert's advice can grant Advantage) as a one-round-skill-challenge.

• More Successes: no Exhaustion and full treatment benefits.
• Equal Successes and Failures: no effect from treatment.
• More Failures: no exhaustion, but botched treatment effects.

If the treatment is Botched, the victim suffers the inverse effect of a successful Check. (For example, a Botched Field Medicine Check increases the Severity by the medic's Wisdom Bonus.)

Simplified Rules

When a victim contracts a Malady, they make a Save against the Malady's DC (the Severity Save) to determine the Severity with which they are infected. Each Severity level affects the victim differently and has different requirements for recovery.
Being exposed to the Malady again forces the victim to reroll the Severity Save. If this new Save results in a worse Severity than the previous Save(s), then the Malady worsens to that Severity.

Recovery Checks

Roll the Malady's listed Save against its DC + Severity. If you fail, suffer the effects of the current Stage (many diseases also become more severe if you fail). If you succeed, the effects of the Malady are halved and you automaticaly expend 1 Hit Die. Roll it. If your Hit Die rolls higher than the Malady's Danger Level + Severity, then you make progress toward recovery (the exact effects are listed in the Malady's stats).
Relatedly, if your Hit Die doubles the Malady's Danger Level, then you make twice as much progress toward recovery.

Resting and Treatment

Resting and proper medical attention can assist with the recovery process. The two stack with each other.

Resting

When the victim completes a Night's Rest or Respite, they can immediately attempt a Recovery Check if the Malady does not already require one at the end of a Night's Rest.
Success: instead of expending 1 Hit Die to fight the disease, they can use a number of HD up to the Bonus from the afflicted Attribute (or double that if it was a Respite).
Failure: if the Recovery Check is required by the Malady (usually for completing a Night's Rest), then follow the rules above. Otherwise, the victim only misses out on this extra chance to recover. There are no penalties for failing this Recovery Check if the Malady did not require it.

Treatment

A creature can also apply medical attention over the course of a Meal or longer rest. To do so, they must attempt a Medicine Check with DC of Malady DC + Stage. A given Treatment can only be applied once per day.
If they succeed:

• Field Medicine (Meal): add the medic's Wisdom Bonus to their next Recovery Check.
• Basic Treatment (Night's Rest or Respite): add the medic's Wisdom Bonus to the next Recovery Check, and the victim can add one of the medic's Hit Dice to the result of their recovery Hit Dice.
• Full Treatment (Respite): in addition to the effects of Basic Treatment, the victim can roll twice as many Hit dice as they would otherwise be able to.

After Full or Basic Treatment, the medic gains 1 Exhaustion Level unless multiple creatures work together to provide the treatment. If they do, each must make the Medicine Check (though an expert's advice can grant Advantage) as a one-round-skill-challenge.

• More Successes: full treatment benefits.
• Equal Successes and Failures: no effect from treatment.
• More Failures: Botched treatment effects.

Botched Treatment

If the treatment is Botched, the victim suffers the inverse effect of a successful Check. (For example, a Botched Field Medicine Check subtracts the medic's Wisdom Bonus from the next Recovery Check.)

Malady Danger Guidelines

Danger Level Comparison

• Danger 4: even a frail wizard, lost and alone in the wilderness, with no treatment whatsoever might be able to recover. Tougher adventurers, or those with a medic nearby, need not fret.
• Danger 7: most adventurers are tough enough to withstand this without much treatment.
• Danger 10: most adventurers will need at least a little treatment to overcome this.
• Danger 12: even the toughest adventurer will need some form of treatment to overcome this malady.
• Danger 15: some form of treatment is required to recover from this. Wizards and similarly frail adventurers are likely in serious danger if they do not quickly get medical attention.
• Danger 20: this malady is very difficult to recover from. Frail adventurers will need thorough medical attention, probably magically assisted, while particularly tough adventurers might be able to get by with minimal treatment. Maybe.
• Danger 25: recovery without treatment is essentially impossible for even the toughest adventurer. Frail adventurers are advised to sprint to the nearest cleric for treatment.
• Danger 30: this malady is a death sentence. Very difficult to recover from, even with proper treatment in a safe place by strong clerics.
• Danger 31+: stars save us all...