The below house rules are for my campaigns, in this case Dark Equestria, but may change if I change campaigns. I am willing to discuss my decisions and even perhaps even change the house rules a bit if given reason to do so.
House Rule 1: All spells with the Evil descriptor cannot be cast by any spellcaster without some chance of corruption, or in other words becoming evil. The percentange chance of this happening is based on level, 1st level spells with Evil descriptor have a 10% chance, 4th spells with Evil descriptor have a 40% chance, 8th level spells with Evil descriptor have a 80% chance, exc. On a list of level spells go here:
https://ponyfinder.forumotion.net/t17-list-of-evil-spells#22House Rule 2: Some spells do not exist or are impossible to recreate in Dark Equestria, or can only be found in the Twilight Librarium either because they are heavily restricted or in development for use by Twilight and a select few others (though it is possible to find restricted spells outside of the Twilight Librarium).
– Wish (this rare spell can only be cast by Celestia, Luna, Harmony, or Starlight Moon). Twilight has tried and failed much to her frustration to cast Wish, though she has created an experimental Limited Wish that only she can use though it doesn't always work.
– All spells that allows travel to, effects, or involves any other plane does not exist, though there is those that theorize the existence of other planes and thus have created some experimental spells (like Twilight Sparkle).
– All Resurrection based spells will be one level higher and have a chance of failure, either not working at all or working but at a heavy cost. A single exception for this is Wish which can be used bring back one that has died without cost (yet only four can cast this spell).
– Summon Monster Spells can only be used if a player comes up with an alternate list of monster for each spell which do not break the above rules (no monsters or creatures from another plan)
– All time based spells (counting mainly Time Stop and Temporal Stasis) are heavily restricted, time magic and spells can only be found at the Librarium.
– Maze, Power Word spells, Death Effect spells, Reverse Gravity, Simulacrum, Geas/Quest, and Magic Jar are all very rare spells that must be found.
– Clone*, (*currently in development and thus does not currently exist), Soul Bind (Does not exist)
House Rule 3: (This is in addition to the ruler for Non-Dexterity) Ponies can wield one single handed weapon with one of their front legs if connected with a strap to their wrist, but only if the weapon is not too large, unwieldy, or awkward for such (will discuss when it comes up). Also remember that some weapons may dull if dragged against the ground, and the possibility of needing to take a balance check when running or walking while under stress or in difficult terrain as this gives the possibility of stepping on or tripping of the weapon.
For the most part ponies will use their mouth to wield their weapons, any single handed weapon can be wielded without penalty that they would normally be able to use based on class. There will be no double handed weapons and instead there will be basic magic weapons that is treated as the double handed weapon (magic weapons with the traits of a greatsword for example but smaller in size).
To speak while wielding a weapon in their mouth a pony must either have a strap to drop their weapon near their neck or a stone/necklace that allows one to speak clearly by a number of means (allowing you to speak verbally or mentally are the most common). Bows and long bows can be used by any pony using their hooves (or magic). Crossbows can be used if braced correctly against something else and pulled back with a ponies teeth or magic (moving their mouth away before firing).
House Rule 4: Some classes will be be limited, banned, or restricted. Classes and prestige classes that will be banned are such because they do not fit in the Dark Equestria Compaign. Classes that are limited are such because logically only a few or only a single race can become it. Classes that are restricted are similar to classes that are limit in that while you might find a wider range of races that can be this class it would still be race for them to be such. Or they could be classes that are restricted in other ways (Wizards, Sorcerers, and Druids).
* Banned Classes: Out of the main classes none will need to be banned, classes from other books might be though, will make a decision on a case to case basis.
* Limited and Restricted Classes: Clerics are limited to only those that worship a deity, you cannot simply worship an ideal to become one. In addition Clerics will be mostly earth ponies, then less commonly pegasus, and very rarely unicorns (most unicorns don't have what is need to be clerics or other divine classes, being to logical and focused on arcane magic for such). Also, Clerics not of Celestia and Luna are watched or even attacked by the Churches of the Sun and Moon. It is illegal in Equestria to publicly be of any religion other then the Churches of the Sun and Moon. Clerics and Churches of Harmony and Starlight Moon are hidden (the latter being few in number and weakened after Starlight Moon's defeated), but the common ponies still know of these two deities. Many ponies in Equestria secretly worship this two deities, though many have given up on Harmony and Starlight Moon.
For the most part ONLY unicorns can be an arcane class, being the only ones that can tap into this sort of magic and are usually Wizards or other learned arcane spell caster of some sort though some are able to spontaneously cast this sort of magic (rarer still are those can cast both forms of arcane magic... the greatest example being Twilight Sparkle). Most wizards never get past level 18, unless they have managed to not be known by that point, as at that point Twilight either talk the wizard into joining her or have the arcane spellcaster killed. That or gain control of them using her Want It Need It spell.
Exceptions to this are Bards which any pony race can be, and rarely Sorcerers (those with unicorn blood and can cast arcane magic will normally be born unicorns, as few non-unicorns are born that are gifted with being able to tap into arcane magic and will always be a spontaneous spellcaster).
Also, there are Paladins that worship Celestia though they will all be Lawful Evil... but because of their devotion to her gain most of the abilities of being Paladins without penalty though some abilities will need to be alters.
Druids are a rare class, few ponies have the closeness need towards nature to become druids, and most never get past level 15 (because at that point Fluttershy will try to kill the druid or make sure the druid doesn't become any stronger). There is also a powerful group of druids and rangers that work for Fluttershy, this group being the main druidic order in Equestria. Thus it is likely any druid in the party will need to have been a member of this order before becaming a druid (thus making the druid known, and watched).
House Rule 5: Many monsters and magical beasts from the Monster Manual will not show up in Dark Equestria at all or show up altered (perhaps weakened), while others will solely be the creations of the beastmistress Fluttershy. Dragons will most likely follow different rules and there will not be much of a 'variety' of dragons.
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House Rule 6: There will be a warning system in place for players that have been causing problems, after a certain point these players will be unable to play in the Dark Equestria Campaign. To learn more go here:
https://ponyfinder.forumotion.net/t18-warning-system