Birthday Party House Rules, Final Draft

Ruleset: 3LBBs + Greyhawk.
Other Books on the Table: Player's Handbook*, Monster Manual**, DMG*** & Carcosa****.
Dice: 20-sided, 6-sided.
Abilities & Saving Throws: 4d6 drop the lowest, assign in order; no minimum for classes; easy peasy modifiers (i.e. >15 +1, <6 -1.) Single Saving Throws as per S&W (Thieves save like Magic-users.)
Classes: Fighter, Magic-user, Cleric or Thief. Sub-classes like Barbarian, Ranger, Paladin, Druid, Illusionist, Monk, Assassin et al are available on request.
Hit Points: 6 + Con mod. at first level, then 1d6 + Con mod. each new level; Fighters get 6 + 1d6 + Con mod. at first level, another d6 + Con mod. at second level and so on.
Races: Standard; those required by players (i.e. wookie) get one or two special abilities by DM's fiat.
Psionics? Maybe Carcosa ones.
Spell Casting: Magic-users memorize spells, then cast, then they can memorize again (even if just one turn has passed since they last memorized a spell.) Point is that to be able to do this, they have to carry their books around, and you know this may be very dangerous. Clerics do the same, but the divinity may not answer their call (i.e. you cure someone, than ask again for another cure and no one is listening to you, fucking jerk.) Point is divinities are just like Dungeon Masters: unpredictable. Clerics need no spellbook.
Equipment: basic class equipment is provided by the DM (i.e. armor and weapon for Fighters, weapon and spellbook for Magic-users, holy symbol, armor and weapon for Clerics, rope, armor and weapon for Rogues), then you get 1d6x10gp to buy whatever you want.
If you want do to something that is not in the rules and I really need to roll some dice rather than just issue a decree: You roll a d20, modified by one relevant ability, and I consult the following table – if you score higher, you succeed.

Difficult 9
Hard 12
Very Hard 15
Nearly Impossible 18
R'u Serious?! 21+

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*Only for equipment.
**I'll use monster stats from Monster Manual. It's way easier to read.
***I'll use To Hit and Item Saving Throws from DMG.
****It's always cool to have Carcosa on the table, and I can also have spawns and droids and cool technological stuff on the spur of the moment. Yeah maybe also Cthulhu if I'm a bastard.