The object never reaches c until it crosses over into a portion of our universe we can't observe. I can show you how energy is conserved for all radius approaching r = 2M (event horizon). Its best to think in terms of total energy increasing rather than mass increasing. In modern relativity mass is an invariant (the same in all reference frames). It is intrinsic energy that makes up an object. Its rest energy. If you want to see the energy conservation for an object freely falling towards the black hole let me know. Pick a distance r=2M + dr from the event horizon. Later on I may know more about the speculative physics inside the event horizon. As of now I can derive the horizon to crunch times but thats it.