Everything

A shapechanged creature retains his original mind and abilities; the new form, of course, might prohibit him from using them – a cat, after all, cannot text accurately on a cell phone even if he knows what he’s doing!

If the new form has certain innate physical abilities (wings, claws, gills, a tail), then the shapechanger can use them naturally; however, abilities that human beings could not innately possess – fire-breath, levitation, poison, etc. – do not automatically come with the new form. A mage can use other Spheres to create those abilities (say, Forces and Prime to conjure fiery breath), but such powers must be “built into” the shapechanging Effect, as described above under The Basics – they’re not automatically “part of the package.”