A DualBeing is simultaneously present in the physical and astral planes. While dual, you can chose whether to use your ST or CH for hitting astrally active things. You can choose to use HT or WL for soaking astral damage (that is, which Tuffness and innate armor values to use). You use the lower of your DX and IQ for dodging and to-hit rolls vs. astral targets. Yes, this makes you terribly vulnerable. Some animals (e.g. most varieties of ShapeShifter) are naturally dual; they get some benefits from long experience which you'll find out if you play one. Naturally dual creatures cannot ever astrally project without killing their physical bodies.