Oh yeah, that reminds me. Particularly important houserule: there is no such thing as an immunity. That goes for players AND monsters. I just find they sap a LOT of the fun out of the game. Creatures that are normally "immune" to anything instead get a great deal of resistance to it. Example:
A creature that is immune to fire gets to cut any fire damage in half (before saves that would limit its damage) and then get to apply an amount of energy resistance that is equal to their HD + 5. Therefore, killing a Medium fire elemental with a fireball is pretty hard to do, but if you meteor swarm it the thing dies just the same. Searing spell would remove the 1/2 damage thing, but not the energy resistance (if all it has is fire resistance, that gets cut in half instead). This "post-resistance" increases to HD +10 at 10 HD, HD +15 at 15 HD and HD+20 at 20 HD.
Things that are normally immune to fear instead get a bonus to their saves equal to +1/2 their HD, and the duration of said fear is halved, rounded up (minimum of 1). Mindless critters act as if afraid though they aren't, really. Same thing pretty much goes for any status effect, as well as death effects. In the event of an effect with no clear duration, i.e "until the target rests again", the standard duration is equal to the CL of the spell or the HD of the originating creature, whichever is lower, in hours.
Creatures normally immune to critical hits halve the extra damage from the crit itself (roll separately). Same goes for immunity to precision damage.
