Between the Sovereign Host, Silver Flame, and the cults of Vol and of the Dragon Below, are there any significant holidays or even a "festive season"?
There are several of them scattered through the Faiths of Eberron. Sharn: City of Towers however lists several of them in one place. In annual order:
- Rebirth Eve in celebration of the winter solstice (Silver Flame) on 14 Zarantyr
- Bright Soul's Day is a Silver Flame version of the Christian All Saint's Day where those who died in service of the Silver Flame are remembered on 18 Olarune
- Tirasday in celebration of the birth of Tira Miron (Silver Flame) on 5 Therendor
- Sun's Blessing in celebration of Dol Arrah on 15 Therendor
- Initiation Day in celebration of the founding of the Church of the Silver Flame on 11 Eyre
- Baker's Night is a celebration of mysterious origin among the Silver Flame on 6 Dravago (in honor of Keith Baker, creator of the Eberron setting, presumably)
- Aureon's Crown on 26 Dravago
- Promisetide is a celebration among the Silver Flame of the Sovereign Host for 'stepping down' in deference to the Silver Flame on 28 Dravago
- Brightblade in celebration of Dol Dorn on 12 Nymm
- First Dawn is a celebration of the Church taking over Thrane on 21 Nymm
- Silvertide is a celebration of the couatl on 14 Lharvion
- The Hunt in celebration of Balinor on 4 Barrakas
- Victory Day in celebration of the success of the Silver Crusade on 9 Barrakas
- Fathen's Fall in memory of one of the heroes of the Silver Crusade on 25 Barrakas (may be specific to Sharn)
- Boldrei's Feast on 9 Rhaan
- The Ascension in celebration of the sacrifice of Tira Miron giving birth to the Silver Flame on 1 Sypheros
- Wildnight in celebration the Fury on the night between 18-19 Sypheros
- Rampartide is a day of fasting and repentance on 24 of Aryth
- Long Shadows is a dark time remembering when Aureon created the first arcane spells, and Shadow with it on the nights of 26, 27, and 28 Vult
- Khyersef is the specific name the Silver Flame uses for 27 Vult because Shadow is strongest then.
Blood of Vol has two special days which are not regular occurrences on the Galifar calendar: the Sacrament of Blood which occurs at irregular intervals throughout the year, and Revelations Day which occurs on 13 Crya (where Crya represents the lost thirteenth month).
The calendar in Sharn also places specific dates on the Day of Mourning (20 Olarune) and Thronehold (11 Aryth) which are secular celebrations.
For 3.5, Faiths of Eberron details holidays for most of the major religions, using the calendar detailed in Eberron Campaign Setting.
Whether, and where, this information was reproduced and/or updated in 4e, I do not know.
In addition to the days listed below, Faiths of Eberron details the life-event (a birth, a death, a marriage, etc.) ceremonies that each faith performs. I have elected not to include that information because they don’t seem to be exactly what we’re asking about, but it’s worth knowing that the information is there.
The traditional calendar (described in this chapter) apparently had 16-day “weeks,” with each day devoted to a particular member of the Sovereign Host or Dark Six, plus one day for the pantheon as a whole. In modern times, the days associated with the Dark Six are instead associated with one of the Five Nations and then the Kingdom of Galifar as a whole.
15 Therendor – Sun’s Blessing. Festival to Dol Arrah, a day of peace when enemies set aside differences
26 Dravago – Aureon’s Crown. Celebration of knowledge, has also become the traditional date for graduation and commencement ceremonies even among secular institutions.
12 Nymm – Brightblade. Dol Dorn’s day, with gladiatorial and athletic contests.
4 Barrakas – The Hunt. Celebration of Balinor; the festivities are exactly what it says on the tin.
9 Rhaan – Boldrei’s Feast. Traditional day for elections (which seems weird considering that Galifar was traditionally a monarchy). Tends to have extravagant parties.
The seven-day week of the Galifar calendar has, in areas with particularly strong Dark Six worship, each day associated with one of the six, and the last associated with the Six as a whole. Dark Six worshipers also recognize six seasons, not the usual four, one for each of the Six. Also, weirdly few specific holidays:
18-19 Sypheros – Wildnight. To the Fury, a night of passion celebrated even by those who do not worship the Dark Six.
26-28 Vult – Long Shadows. Three days devoted to the Shadow and dark magic.
Church of the Silver Flame
The first day of the week is the Day of Cleansing Fire, a weekly holy day where a single meal is replaced by a period of prayer. Obvious real-world parallels are obvious. Aside from that, they have thirteen holidays:
14 Zarantyr – Rebirth Eve. The winter solstice and when the Church celebrates a new year. Entails staying vigil through the longest night of the year, and then resting or celebrating the fact that days will be getting longer and nights shorter from then on.
18 Olarune – Bright Souls’ Day. Celebration of martyrs; families of martyrs re-enact the funeral rites, everyone else sing general paeans, and no one uses artificial or magical light, accepting night as the martyrs accepted death.
5 Therendor – Tirasday. Tira Miron’s birthday, and the start of the planting season.
11 Eyre – Initiation Day. Anniversary of the Church declaring itself a new religion and work beginning on the first cathedral. Beginning new churches or cathedrals is usually scheduled for this day, as is graduation from seminaries.
6 Dravago – Baker’s Night. An awesome festival where all faithful bakers and confectioners make magnificent pastries and similar treats, given out to the rest of the community. No one has any idea what this is to celebrate or where the tradition came from, even though it is certainly from the earliest days of the church.
28 Dravago – Promisetide. Wherein the Church honors the Sovereign Host for creating the world that the Flame would later complete, and for stepping down to allow the Flame its rightful place. The existence of this holiday does not do the church any favors among followers of the Sovereign Host.
21 Nymm – First Dawn. Anniversary of the church’s assumption of Thrane’s government, wherein secular officials are prayed for.
14 Lharvion – Silvertide. Holiest day of the year, commemorating the couatl’s sacrifice that banished the fiends, ended the Age of Demons, and brought the Silver Flame into Eberron. The devout spend the entire day in church.
9 Barrakas – Victory Day. Commemoration of the successful conclusion of the Great Purge. Children celebrate with mock battles and toy weapons, but adults do attend sermons which are supposed to cover, at the least, the defeats and questionable methods of the templars as well as their triumphs.
1 Sypheros – The Ascension. Another day dedicated to Tira Miron, thanking her for taking on her position and seeking ways that they can help their communities.
25 Sypheros – St. Valtros’s Day. Anniversary of the birth of the first paladin devoted to the Silver Flame (as opposed to paladins of other faiths who converted). He gets a mention during church services but it isn’t really a major holiday beyond that.
24 Aryth – Rampartide. Kind of like the opposite of Rebirth Eve, a day of fasting and repentance, steeling the faithful against the shortening of days, lengthening of nights, and the winter that is to come.
27 Vult – Khybersef. Literally the church’s reaction to the Dark Six holiday of Long Shadows, when the faithful spend the night in intense prayer as vigil against the Shadow. Quests and crusades often begin on Khybersef.
I have no idea why Faiths of Eberron devoted massively more page space to the Silver Flame’s holidays than any other faith.
Blood of Vol
The Blood of Vol is a weird, weird faith. Not just because of their particular beliefs, nor because of the secret conspiracy behind the faith, but also just in how they handle holidays.
(no set date) – The Sacrament of Blood. This is just a thing that happens at irregular intervals, dictated by the Crimson Covenant and the timing of which tends to mystify even the leadership of local cults. Every member of the congregation cuts him- or herself with a ritual dagger known as a bloodfang, and adds a drop of his or her blood to a chalice. This blood is secretly stored and transported around Khorvaire for the various necromancy projects of the Blood as an organization.
13 Crya – Revelation Day. Crya is the “lost” 13th month, which of course ties back into the lost 13th dragonmark, Vol’s own Mark of Death. Doesn’t exist on the modern calendar, the date is based on the older elven calendar that had thirteen months. Basically, the Sacrament of Blood in reverse: each congregant drinks from a filled chalice of blood. The blood has been magically made safe to drink, and also altered with various psychotropic substances so that everyone enters into a hallucinogenic “blood trip.”
The sects vary a lot, but Faiths of Eberron does state that they celebrate the solstices and equinoxes. During the autumn feast, a special ceremony of thanks to Oalian takes place, which makes it the most important of the four. Involves a mildly alcoholic drink made with pinches of soil from each druid’s home area, and poured out some distance from Oalian so the greatpine’s roots can drink it.