I've done a similar post fairly recently, but this is my more up-to-date version!
- I use Castles & Crusades as the basis for the rules.
- All Target Numbers start at 15. No Primes and Non-Primes at 12 or 18 and levels are not added to rolls. With each level gained, the TN goes down by 1 (Replacing the 'Level as bonus' method). Modifiers to rolls and/or TN otherwise apply the same way as written. (I still have not decided at what point the TN stops dropping, probably somewhere between 4 to 2. My players are far from being there yet anyway.)
- I will not be using the rule from 'Castles & Crusades' where a monster's number of HD becomes a penalty to Saving Throws. If I include a monster with an attack that players have to save against with a penalty, I will consider it a monster of higher HD than it is for the purposes of handing out XP for killing it, as per the guidelines in 'Crypts & Things'.
- To compensate for the lack of Primes, Humans gain a +10% bonus to XP. (I grabbed the idea from Basic Fantasy Roleplaying.) Half-Elves raised by Humans gain +5% as a bonus to XP.
- I use the encumbrance rules from Lamentations of the Flame Princess.
- For the Wizards and Illusionists, I use the spellcasting rules from Lamentations of the Flame Princess (except for the time it takes to prepare spells each day) but use the spell list from Castles & Crusades as the 'default' spell list. That said, I freely grab spells from all over the OSR and OGL.
- For the Barbarian class, the version from Tales of the Grotesque and Dungeonesque is used instead.
- Experience Points: 1 GP = 1 XP if it's successfully brought back to civilization (as in LotFP), XP for Monsters from Crypts & Things (The main rule for monster XP, not the optional one I thought of using in my previous house rules post, although I am using those for a limited time during a gladiator-themed adventure. Seems appropriate.), XP for Traps as in Machinations of the Space Princess, Story and RP XP rewards from Castles & Crusades.
- Class Skills are rolled at +3 and any class can attempt any skill as in Crypts & Things. That said, I've added that skills that are not Class Skills are rolled at -3. (Ironically, we end up with a modifier difference of 6, the same difference Castles & Crusades normally has between Primes and Non-Primes! Just a fun fact. -If you're a total geek like me.-)
- I have decided not to use Class-and-a-Half but I apply some of its rules to Multi-Classed characters:
- Wizards and Illusionists with an armor proficient class can cast in armor but their armor's AC bonus also becomes a save bonus for the target's Saving Throw. (Magical bonuses on an armor do not apply to this.)
- I use the Class-and-a-Half rule for Monks, Rangers, Rogues and Assassins aligned with armor proficient classes.
That's all for now! I'll also use some more specific rules from a variety of sourcebooks depending on the current adventure but the above are the main ones. I'd love some feedback from fellow players and GMs to see what you guys think.