putting an effective spell level to SP/SU abilities

[Raishoiken]

As far as effects like Wish and Miracle that can duplicate spell effects or effects equal in power are concerned, would it be appropriate to have a creature's CR/2 substitute for the spell level since it'd be about as rough as rough can be an estimate?

[MaxiDuRaritry]

DCs tend to have saving throws of 10 + 1/2 hd + Cha or Con mod, while spells have DCs of 10 + spell level + the appropriate ability mod.

So the logical thing would be to compare them and realize that effective spell level equals 1/2 the creature's hd.

[NigelWalmsley]

You definitely should not set effective spell level to HD, because there is no correlation between HD and power level, let alone between HD and how dangerous any individual SLA is. Half CR is the best you're going to do as a general rule.

[ExLibrisMortis]

For spell-like abilities, you should just use the equivalent spell. E.g. a 5 HD/CR 8 ogre mage gets cone of cold--that's still a 5th-level spell no matter what, and HD and CR don't enter into it. Don't create a new spell bargain bin, there's enough of that already.

For supernatural abilities, you should probably favour CR over HD for the reasons NigelWalmsley gave, but it's more accurate (and more work) to look at each ability individually. I would definitely not suggest that you can emulate a choker's Quickness as if it is a first-level spell, for instance, or even a third-level spell, even though chokers are only CR 2. I'm assuming here, of course, that Quickness can be emulated in some sensible way without introducing a crapton of homebrew statistics, which is a stretch.

[Melcar]

As far as effects like Wish and Miracle that can duplicate spell effects or effects equal in power are concerned, would it be appropriate to have a creature's CR/2 substitute for the spell level since it'd be about as rough as rough can be an estimate?

Sorry, could you elaborate? I simply dont understand the question...

[NigelWalmsley]

I would definitely not suggest that you can emulate a choker's Quickness as if it is a first-level spell, for instance, or even a third-level spell, even though chokers are only CR 2. I'm assuming here, of course, that Quickness can be emulated in some sensible way without introducing a crapton of homebrew statistics, which is a stretch.

On the one hand, yeah, that'd be dumb. On the other hand, you can already do way dumber stuff with Wish. On the gripping hand, you're almost certainly correct to imply that doing that wouldn't actually work in any real sense.