CharlesRyan
Adventurer
Howdy, Durnscarniepals, and welcome to EN World. This is a great place for the sort of input you're looking for, so i hope you'll visit often!
I happen to have a bit of experience with d20 Modern, and I'll second pawsplay's analysis. In my own games, I've found it's a pretty good rule of thumb to bump the CR of any D&D creature with substantially supernatural powers by +2. You'll also want to watch out for (alter, discard, or use sparingly) any monster capabilities for which your PCs will have absolutely no countermeasures--like level drain, for example.
Hope that helps!
I happen to have a bit of experience with d20 Modern, and I'll second pawsplay's analysis. In my own games, I've found it's a pretty good rule of thumb to bump the CR of any D&D creature with substantially supernatural powers by +2. You'll also want to watch out for (alter, discard, or use sparingly) any monster capabilities for which your PCs will have absolutely no countermeasures--like level drain, for example.
Hope that helps!