All of the Fallen are unique beings, more unique than the angels they fell from or the fiends that they will reside among. Hence, you will be allowed to build your Fallen in most any manner.
You will be able to use the ARG to build your race, but may select any of the 'base forms' for Eidolons as a body type.
You gain 30 points to buy racial stuff from the ARG with, though ability score bonuses are banned and AC bonuses cap at +4.
You also gain the equivalent of 10 Evolution Points from the Eidolon list to add to your character. These points may be spent on anything but ability score bonuses and AC/SR/DR.
Arms cap at 3 sets (Six arms), so there are no 'hundred handed ones' in the group.
Each character also has the power of flight. You choose either Winged Flight or Supernatural Flight. Winged Flight functions at base speed x2 with Good Maneuverability, functions in antimagic zones, gives you wings, which allows you to select the Wing Buffet natural attack from the Eidolon list of abilities, should you decide to spend points on it, but does not function if you are unable to use your wings somehow. Supernatural Flight functions at base speed x3 with Perfect Maneuverability, allows you to move in any combination of directions while airborn, and can be used even if physically restrained or immobilized, but is completely negated in areas of antimagic.
You also gain immunity to ONE type of energy damage of your choice, chosen at character creation. Choices include fire, cold, electricity, acid, sonic, negative energy, and positive energy.
Your type is Outsider (Evil, Fallen).
You also have several powers and limitations as Fallen, but it is up to you to discover those in-game. Benighted Prince spoiled a few of the weaknesses in the interest check, but no more shall be spoiled