I've just finished re-reading the first Shira Calpurnia novel and the way the large religious festival featured in the book played merry hell with her Arbites investigation had me thinking. Wouldn't it be a great theme for a game of Inquisitor (and all it's variant flavours...), Necromunda or any other skirmish set in the 40K Universe to have the edicts of a local religious festival interfere with the actions of your warbands?
So I thought up some possible (Imperium) religious observances and the effect they could have on a game:
(Several of these require the presence of civilians on the battlefield. As there are preciously few/no models for 40K civilians, you may want to substitute them with tokens, stand up paper counters or such. The amount of civilians present can be used to tweak/determine the difficulty/severity of the disruption of an event.)
-Festival of the Emperor's Ascension/Unification Day: A major exuberant festival is going on today, the streets and buildings are awash with people in raucous celebration. There are drunk, exuberant civilians everywhere (You will need lots of civilian models for this) getting in the way, blocking movement and line of sight with their random movements. Depending on one's skills and approach they can either hinder stealth (too many eyes everywhere) or aid it (hiding in the crowd). Maybe there is even a parade or floats?
-Military Observance: The military is engaged in a religious event at this moment, so all PDF/Imperial Guard/Navy personnel are effectively restricted to quarters. No Military/Navy/PDF personnel may be fielded by any warband.
-The Vigil/Quiet contemplation: This is a day of quiet introspection and prayers, loud noises are forbidden, enforced by the Ecclesiarchy/Sororitas. No firearms, explosives, vehicles or similar sources of noise may be used. Breaching this edict will risk being detected/reported and bringing a mob of militant Preachers/Frateris Militia/Arbites or Sisters of Battle to the area to enforce (violently!) the peace and quiet!
-Detestation of the Oathbreakers: On this day, the people commemorate a certain betrayal in the planet's past and assert their own faith by ritually reviling those past traitors. One or more items, clothing or colours associated with the traitors are taboo on this day. Certain individuals, as penitence for some sin, are forced wear one or more of these taboo item and represent the detestable oathbreakers on this day. It is considered to bring good luck to beat and otherwise abuse these people on this day... Determine a random type of item, clothing or a colour. Any model on which said item or colour is present runs the risk of being randomly assaulted by passing by civilians or religious figures.
-Incense for the fallen/Burning off the sins: On this day, religious edicts demand the burning of massive amounts of heavy, cloying incense or specially treated parchments on which citizens have written their sins to confess and burn off. The heavy smoke fills the battlefield, impairing vision and possibly, in patches of very heavy smoke, even breathing... Could be combined with Day of Atonement.
-Day of Atonement: A day of self-flagellation. The streets and buildings are filled with civilians in religious extacy, beating and whipping themselves, or passed out from exertion and blood loss. On the battlefield there are several civilians moving in random directions, getting in the way, as well as a large number of passed out people underfoot to trip over, hide behind, prevent from getting harmed by the fight... To make things really unpredictable, you could have civilians randomly falling down from exhaustion or getting back up again to continue their self-flagellating roaming!
-Religious procession: Determine a random path through the battlefield. This is the route of one of the many religious processions of this day. During the game this path will be travelled along by priest bearing reliquaries, processions of pilgrims and other religious hangers on/devoted civilians. The path may or may not be cordoned off by physical barriers, (ritually) armed guards or other means. Maybe crossing the path of the procession is simply considered taboo and you risk assault by enraged religious bystanders?
-Minor Observation: This day is dedicated to a religious observation that has a negligible effect on the game (People must have polished their Aquila symbols, no left socks or blue underwear may be worn, none may be seated on a padded cushion, whatever, think of something). However, the Ecclesiarchy still demands adherence to this observation with the utmost gravity. As such on this day, patrols of Arbites/Sororitas/Preachers with retinues may at random search any person, vehicle or building to ensure the particular edict is followed to the letter. It's hard conducting a battle or covert observation when there is suddenly a priest loudly demanding everyone remove their left boot for an inspection under the Edict of Sinful Socks!
-Hearing of Confessions/Begging of Benediction: On this day any member of the Ecclesiarchy or other religous organisations/individuals (Priests, Sisters of Battle, Commissars, etc. Maybe even Space Marines?) may be approached by any individual to hear their confession/get blessed by/touch for good luck. When such an individual is present on the table, civilians in line of sight will attempt to move into base to base contact with them. You could optionally rule that hearing a confession/speaking a benediction requires a civilian to spend a full turn in base to base contact with said character, if you want to be really devious.
-The Purge: A day of ritual lawlessness, there are armed, violent mobs roaming about all over the game table looking for someone/anyone to beat up...
-Omnissiah Vigil: All the Adeptus Mechanicus are cloistered away on one of their inscrutable observances. No Mechanicus personnel may be fielded by any warband. In extreme cases this religious event may even forbid the use of any technology at all!
-Religious Curfew: When the curfew starts, no-one may be outside on pain of death/excommunication/arco-flagellation, something horrible. People are bound to provide hospitality to anyone seeking refuge when the curfew starts. Randomly determine if the curfew is or isn't in effect at the start of the game. At a random point during the game this will change, with the curfew either coming down or getting lifted on from that turn on. Note that even if the game takes place inside, this can affect the game as a building may suddenly get flooded with bystanders seeking to obey the curfew!
-Day of Transition: Choose two religious observances. The first is active at the start of the game, at a randomly determined point in the game (e.g. 4+ at the start of each turn), this observance will be replaced by the second one.
-Religious High Day: Several observances are in effect on the same day!
Enforcement: As there is no division of church and state in the Imperium, you could rule that there are random patrols of Arbites/Frateris Militia/Sisters of Battle or even other factions to enforce that day's edicts. Any game could have a chance to encounter such a patrol on the table.
How to use:
You could decide to randomly roll if a there is a religious event taking place at the start of a game, and make a chart to determine which particular event is going on at that time.
In a GM-run or narrative game, you could determine the itinerary of the entire festival beforehand and only give the information to those parties already familiar with the planet's culture or in good standing with the Ecclesiarchy beforehand. Other parties will have to find out on the day itself...
Like in the book, a group that is in good standing with the local religious orders (So filthy mutant, heretic or alien deviants need not apply...) could beg indulgences that would excuse them from certain observances. Though those come at a price, either resources, other restrictions, compensatory observances at another time or perhaps even being sent on a Quest or pilgrimage?
Have fun, and if you try this, let me know how it went!