Here is an example of a defensive pleading (redacted) based on Virginia law that addresses the efforts by loan servicers (here, Aurora) to obfuscate the issue of who is entitled to enforce your mortgage debt by way of foreclosure, as well as such servicers' efforts to conceal the possible lack of actual ownership of the loan by the entity that claims to be the beneficial owner.
Notice that much of the argument is rooted in the language of the deed of trust itself and the distinctions it draws between the servicer and the beneficial owner of the debt.
This pleading (kind of like a motion to dismiss) resulted in Aurora's withdrawal of its lawsuit, as I reported earlier.
I believe it is not a stretch to say that a similar challenge can be mounted against any attempts by MERS to take your property by way of foreclosure.
The pleading can be found here.