Lots of questions about this trait. I have some assumptions on how it works but I'm not going to write them to avoid biasing anyone's answers.
Does the model need to know these powers already to combine them? If so do you pay for them twice? (once for the powers and once again for the cost of abyssal weapons)
If not what are the rules for picking these powers? Does the model need to have traits from the domains of these powers, following traditional power selection rules for fey?
If you can choose to take powers you do not already know and combine them for abyssal weapons are you considered to then know those powers for the purposes of taking tier 2 powers from their spheres of influence or is the abyssal weapon power something else.
It is called abyssal weapons but does not actually call out any restrictions on what can be imbued. Could you combine two powers that imbue armor as an abyssal weapon?