If Regina tried to have Daniel reanimated by Dr. Whale – and he succeeded but Daniel came back mainly physically (no cognitive abilities or memories of Regina) …That would explain why the actor playing Daniel was filming (I think it was for the fifth episode). We know from Jefferson how she treats deals, so if Daniel wasn’t back 100% – I’m beating Regina never paid up her side of the bargain. Could that be part of the reason he was the first member of the mob to get his hands around her neck?
We also know how Regina likes to take people’s hearts: the one organ Daniel would be in need of to become Frankenstein’s monster…Another great theory GoldenKey! 😀