Fun with Org Mode Agenda Views

%%(org-anniversary -1166 01 05) Today is Setting Orange, the 5th day of Chaos in the YOLD %d. Celebrate Mungday.
%%(org-anniversary -1166 02 19) Today is Setting Orange, the 50th day of Chaos in the YOLD %d. Celebrate Chaoflux.
%%(org-anniversary -1166 03 19) Today is Pungenday, the 5th day of Discord in the YOLD %d. Celebrate Mojoday.
%%(org-anniversary -1166 05 03) Today is Pungenday, the 50th day of Discord in the YOLD %d. Celebrate Discoflux.
%%(org-anniversary -1166 05 31) Today is Sweetmorn, the 5th day of Confusion in the YOLD %d. Celebrate Syaday.
%%(org-anniversary -1166 07 15) Today is Sweetmorn, the 50th day of Confusion in the YOLD %d. Celebrate Confuflux.
%%(org-anniversary -1166 08 12) Today is Prickle-Prickle, the 5th day of Bureaucracy in the YOLD %d. Celebrate Zaraday.
%%(org-anniversary -1166 09 26) Today is Prickle-Prickle, the 50th day of Bureaucracy in the YOLD %d. Celebrate Bureflux.
%%(org-anniversary -1166 10 24) Today is Boomtime, the 5th day of The Aftermath in the YOLD %d. Celebrate Maladay.
%%(org-anniversary -1166 12 08) Today is Boomtime, the 50th day of The Aftermath in the YOLD %d. Celebrate Afflux.

%%(org-anniversary 1957 5 24) The Glorious People's Republic of Treacle Mine Road: "Truth, Justice, Freedom, Reasonably-Priced Love and a Hard-Boiled Egg!"

%%(org-anniversary 0 12 23) Christmas Adam. Comes before Christmas Eve and is generally unsatisfying.
%%(= 0 (calendar-days-from-easter)) Celebrate the rising of an undead horror from his tomb...

"Christmas Adam" came from a tumblr thread years ago.

"Celebrating the rising of an undead horror" came from a conversation between Charlie Stross and Nicholas Weaver on the Fediverse.

For the later we need a helper function to calculate the Date of Easter.

This is from the Org Mode FAQ: 17.8. How do I schedule events relative to Easter Sunday? Which points at da-kalender.el

;; from https://github.com/soren/elisp/blob/master/da-kalender.el
;; Copyright (c) 2018 Søren Lund <soren@lund.org>
;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 3 of the License, or
;; (at your option) any later version.
(defun calendar-easter (year)
  "Calculate the date for Easter Sunday in YEAR."
  (let* ((century (1+ (/ year 100)))
         (shifted-epact (% (+ 14 (* 11 (% year 19))
                              (- (/ (* 3 century) 4))
                              (/ (+ 5 (* 8 century)) 25)
                              (* 30 century))
                           30))
         (adjusted-epact (if (or (= shifted-epact 0)
                                 (and (= shifted-epact 1)
                                      (< 10 (% year 19))))
                             (1+ shifted-epact)
                           shifted-epact))
         (paschal-moon (- (calendar-absolute-from-gregorian
                           (list 4 19 year))
                          adjusted-epact)))
    (calendar-dayname-on-or-before 0 (+ paschal-moon 7))))
(defun calendar-easter-gregorian (year)
  (calendar-gregorian-from-absolute (da-easter year)))
(defun calendar-days-from-easter ()
  "When used in a diary sexp, this function will calculate how many days
are between the current date (DATE) and Easter Sunday."
  (- (calendar-absolute-from-gregorian date)
     (calendar-easter (calendar-extract-year date))))

We can then schedule things relative to Easter:

Good Friday

<%%(= -2 (calendar-days-from-easter))>

Easter Sunday

<%%(= 0 (calendar-days-from-easter))>

Easter Monday

<%%(= 1 (calendar-days-from-easter))>