How would this effect CR?

[Geiger Counter]

I want to replace all creature's ability drain with equal ability damage. Also I want to make all creatures with energy drain that is permanent only last 24 hours. Also I want to replace any creature with a save or die ability or flesh to stone with doom and a progressive flesh to stone respectively, like in final fantasy where you have a limited amount of time to kill the creature who cast it before the spell takes full effect.

[Baron Corm]

I'm not sure that the first two would affect CR, since neither of those things affect the actual battle much. Whether you have 0 Wisdom from drain or damage doesn't really matter until the fight is over. Whether or not your negative levels disappear later in the day doesn't affect you in combat.

Turning save-or-dies into doom is a big one, though. This is because doom is a very different effect. If you turned save-or-dies into save-or-loses, giving long-term paralysis, stunning, or cowering, then the CR is preserved. Preserving the spell descriptors would make it nearly seamless, so that the same things are immune or not immune to the spell.

For the flesh to stone effect, as long as there are heavy penalties while the person is being turned to stone, the CR should again be the same. Heavy penalties meaning as good as dead... can't move or act, or maybe just a 5 foot move action and a standard action with -10 on all rolls.

Now I was assuming that your goal was to make combat less deadly, but if the goal was to make the actual abilities less encounter-ending, then I think you could turn save-or-dies into high Constitution damage (or Strength or Charisma if you want combat to be less deadly), and flesh to stone into gradual Dexterity damage each round.

The CR lowering on this depends entirely on how exactly you go about changing the abilities, and the monster you're changing. If you took a monster whose only trick was implosion and you turn it into doom, it's significantly lower. If you took a monster with hold person, and turned its implosion into 3d6 Constitution damage, the CR might be lowered by 1, or none.

[ericgrau]

The CR should decrease not because the fight is any easier but because the PCs are paying less xp and gp after the fight, they should get less xp and gp from the fight. Guestimate how much they would have paid and how much you need to reduce the CR so that they "lose" this same amount. Make a mental note that the fight is still just as hard as before, so that you don't send the PCs against anything too tough.

[Lord Vukodlak]

Its really a case by case basis on some monsters its more important then others.

The energy drain on a vampire sorcerer probably doesn't mean much if he spends his fights casting spells. But for a Bodak its death gaze is everything.

I believe what he is trying to do is first, make it easier for a party to get by without a cleric capable of casting restoration. Druids and bards can heal, but they can't undo level or ability drain.