Quote Originally Posted by T.G. Oskar View Post
Though, be swift to recall: ability damage stacks, while penalties from the same source usually don't stack. You can pretty much kill enemies from several attacks with a Wounding weapon, but you can't kill an enemy from two different uses of Ray of Enfeebling. Usually, as a rule of thumb, you can argue that penalties tend not to stack; a Touch of Idiocy coupled with a Ray of Stupidity could be argued that don't stack (at least I know of DMs that won't allow them to stack), but RAW they would stack. Two consecutive Touches of Idiocy on the same target definitely won't stack. But, a cast of Bestow Curse to grant a Dex penalty and Shivering Touch WILL most definitely stack and are excellent tactics.
Are you trying to imply that two Fireballs cast on the same creature would not stack? Damage is not a penalty, and there is no question of stacking involved. Damage occurs instantaneously, it changes the value of the target's HP or ability score to a new value until it is healed back. It doesn't matter how their HP or ability score got to that value, more damage regardless of the source will always be able to affect it. Penalties have a duration, cast one Ray of Enfeeblement and they have a dispellable debuff that can be tracked, so a second casting will not stack. Damage to an ability score such as Ray of Stupidity has no ongoing spell effect, it instantaneously changes the ability score to a new value until healed, and a second effect that applies a penalty will definitely stack with it.

As another example, say a PC with 30 HP gets attacked by a Wight. They take 4 damage, down to 26, and gain one negative level, which imposes a -5 penalty to their HP. That PC now has 21 hp, their max HP is 25 due to the negative level and any HP damage they take will be subtracted from their current total. There is no argument that additional damage will not stack with the HP penalty from the negative level. Just the same, a character can have both a penalty to an ability score and damage to an ability score. Multiple penalties may not stack, but damage is not a penalty and stacks with everything.