The Reaper's Due
Little remains of those settlements where the Black Death has passed through. Hasty burials make a mockery of the sacraments and set a feast for the crows. Once prosperous provinces have been laid waste, and the lord of the land hides away – secluded in his hilltop fortress, hoping the plague will pass him by. Wiser princes took precautions, and didn’t waste the revenues from more prosperous years.
But, in time, all must pay The Reaper’s Due.
The Reaper’s Due expansion highlights the historic importance of epidemics and disease in the Middle Ages, especially the Black Death – an outbreak of the Bubonic plague that may have killed a third of the population of Europe. It introduces many new systems and features to what is already the richest medieval tapestry in gaming:
- Epidemics Improved: As diseases spread from province to province along trade and sea lanes, they lower your manpower and sap your wealth
- Hospitals and Royal Physicians: Prevent the outbreak of disease in your kingdom, and make sure your courtiers have access to the latest in Dark Ages Medical Science
- Prosperity and Royal Focus: Well-managed provinces in peaceful kingdoms will pay huge dividends in gold and levies
- Seclusion: Shield yourself from the diseases tearing your kingdom apart, even if it means ignoring the plight of your people
- New Event Chains: Is the new epidemic the End of Days? Is there someone else to blame for these horrors? Are there supernatural origins or solutions to the world’s problems?
The expansion adds a large number of small features and mechanics around the theme of death, diseases and epidemics:
- Symptoms: characters no longer simply become ill through an event, but instead receive one of a variety of symptoms (Cough , Fever , Diarrhea , Vomiting , Headache , Chest pain , Rash , Cramps , Abdominal pain , Fatigue , Malaise ) and over time it will either evolve into a full blown disease, or will simply pass.
- Court Physician is a new minor title which you can give out to a well-learned person which makes them responsible for diagnosing and treating illnesses in your court.
- New death screams.
- Epidemics can now spread along the Silk road when present, and are more likely to spread to rich and coastal provinces while being less likely to spread to poorer inland areas. They will cause depopulation on provinces even after it has died out, reducing tax incomes, levy/garrison sizes, and supply limits. 
- The Black Death is larger and more deadly, and gets a chance of major outbreak to occur 200 years into any game, regardless of start date. After a major outbreak has happened the disease becomes endemic and may break out again, but likely on a smaller scale.
- Ways to defend against epidemics: seclusion of a character's court in his castle, or building Hospitals (new holding type similar to Trade posts or Forts) to increase the disease defense level.
- Prosperity system: as opposed to Depopulation, provinces which have not been besieged, raided, or ravaged by disease for a long time will begin to Prosper, and gain certain bonuses- such as extra tax income and faster replenishment of levies. Independent dukes or higher can set one of their Demesne provinces to be their Crown Focus for additional yearly increase and events.
- New narrative events such as The rise of a Prophet of Doom, A general belief that the dead have returned to walk the earth and attack the living, or Panic based on a solar eclipse, or the quest for Eternal Life.
- New maimed traits (One-handed, One-legged, One-Eyed, Disfigured, or Mangled) to replace the generic maimed , and some associated portrait frames. The health penalty from most of these traits is replaced by a Severely Injured trait with penalties but will be lost after some time has passed.
- Make demands of vassals: ask vassals individually to end their wars with each other, and ask vassals to return to gavelkind succession.
- Punish prisoners in new ways: Humiliate, Torture, Mutilate, Bad poetry and Consume (if cannibal). 
- Recruit prisoners into your court
- 50 new nicknames: 'One-Eye', 'the Frog', 'the Cannibal', 'the Hideous', 'the Resilient', etc.
- 31 execution methods, including Hanging, Crushing, Sawing, and Bear.
- Reactions events to the death of lovers, friends, and rivals
- Events around cats
Free patch 2.6 features:
- Call to arms: automatic call of allies into war, introduced in patch 2.5, will be reverted. Declining a call now has very serious consequences:
- The alliance and the non-aggression pact are broken.
- You lose half your current prestige, plus 200 (same as truce breaking.)
- Adds an "Alliance Breaker" character modifier lasting 15 years that lowers the opinions of all vassals by -10 and all foreign rulers by -25.
- You get a -50 opinion penalty with the calling ruler and his or her close family (including the spouse that allowed the alliance in the first place.)
- Game rules: in-game configuration of some defines, without requiring to use a mod. Some options will disable achievements.
- Revised succession screen, with epitaph of departed character and brief introduction to the new one
- New decisions for defensive pagans:
- Devout warriors to defend against an enemy of a different religion,
- Ancestor worship to ask your ancestors for help or advise with some part of your life
- For Germanic pagans:
- Improved versions of the Viking trait: Ravager and Sea king
- Valhalla-bound trait, equivalent of Crusader for great holy wars.
- Shieldmaiden , warrior women bodyguards who can also be assigned as commanders or marshal.
- More female advisor options: close relatives of a ruler with high stats, and talented woman arriving in court.
- Flanders is now part of the kingdom of France, and the AI king of France will no longer create the Kingdom of Aquitaine unless needed for Francia Empire creation requirements.
- Tweaks for nomads of Horse Lords expansion:
- Character finder new icons to indicate whether characters will move to your court, and if they are outside of diplomatic range.
- Continue button on the launcher to load directly into your latest save game.
- A combination of game optimizations, resulting in a 30-50% speed improvement, and with far smaller annoying pauses:
- Uncompressed saves are smaller, which reduces compression and write times
- Saves are saved more efficiently
- The processing of things is done across the year rather than at the end of each year, avoiding the noticeable pause
- The map rendering is faster
- Some unnecessary map or UI refresh triggered for non-outdated things are removed
- Several computations that were single-threaded are now multi-threaded
- Some performance-intensive computations are improved
- The number of randomly generated characters is reduced, and unnecessary characters are eliminated more aggressively
- Some modding suggestions.
- The inability to disable Paradox's data tracking, and an EULA updated to reflect that fact
- Expansion was originally named <Secret DLC> in Developer diaries, as it hadn't been announced yet.
- The namespace used for DLC events is "RIP" (Rest in peace).
- For death screams, leek and celery were used to recreate some “sweet” and intense bone cracking sound effects, while the pepper and salad were to create a “slow crushing” sound effect.
- After The Reaper's Due, another two (or even three) expansions are planned before the development stops. "There are still some blanks in the Old World; rulers you cannot play and regions not yet covered..."
- Crusader Kings: Chronicles gamebook will unlock "a song and two event chains".
- Meneth worked on patch 2.6 optimization and modding features, as an intern in Crusader Kings 2 team.
- The Reaper's Due was the first DLC with David "Darkrenown" Ballantyne as Game Designer.
- The Reaper's Due is Here!
- Paradox Announces When The Reaper’s Due in Crusader Kings II
- Development Diary #2: Get sick and die
- CKII - Development Diary May 17th - We don't talk about the dead
- CK2 Development Diary #7: Get Sicker and die harder
- CK2 Development Diary #8 Life goes on
- CK2 Development Diary #10: Live long [yet futilely] and prosper
- CK2 Developer Diary #11: The End of Days
- CK2 Dev Diary #12: The Maim event
- CK2 Dev Diary #16: Man's inhumanity to man
- CK2 Dev Diary #17: Crusader Cats
- Development Diary #4: Don't Call me Shirley
- CK2 Dev Diary - The Rules of the Game
- CK2 Development Diary #9 The secret to success
- Crusader Kings 2 DD#13: Pagans, advisors, and warrior women
- CK2 Dev Diary #15: Assorted cool things
- CK2 Dev Diary #18: Optimization and modding
- CKII - Development Diary May 17th - We don't talk about the dead
- Crusader Kings 2 DD #14: The Road Ahead
- Gamebook Crusader Kings: Chronicles Available Now!