This was all in Reggie'a head from the start, correct? I had to go back and watch 4 again and the scene with Scrimm telling Reggie "it's all in your head" seems to ring true in Ravager.. it was all Reggie and his dementia... I was so confused with the ending and stilll not 100% sure how to take it.
That's one perfectly valid interpretation but not everyone is making it. I'm sure not. Consider that multiple realities means multiple Reggies (and Mikes, and Jodys, etc.). Basically, as always, it's up to the viewer to decide.
There's a point that needs clarifying for me about that quote from IV. "Ice Cream man, it's all in his head." I was sure I heard Angus give a definite emphasis on "his", at which point the films cuts to a brief shot of Mike. Mike has a golden orb in his head which the Tall Man wants. Am I right about that? I don't know for certain whether tTM was referring to Mike or Reg.
So Reggie, while in a coma, dreamed he had dementia where he imagined that Mike dreamed of the events of the first film that was also dreamed by Liz, and even after he died, the dream continued. Inception's got nothing on that.
If you think about it, the multiverse theory makes the most sense, and also explains why the different movies take place from different characters' points of view, so it can't all have been Reggie. The reality where Reggie had dementia was just another alternate universe where the Tall Man never came, and, as Mike explained, when these realities got close, they began to overlap, which is what happened with Reggie.
No, hartman stated in the bluray that there are 3 realities. when reg and old reg go through the gateway they merge. later reg from part 4 merges with them as well because he was on that gateway table where his mind was crossing over with theirs. from this point their realities keep jumping from one to the other. One reggie died, the others lived on. Don on the other hand loves the dementia thing but prefers to let the phans come up with their own theories.