with the monster senario you'd probably have to contend with alot of tissue rejection.
Exactly...which is why you'd be better off trying to reanimate a whole, intact corpse than some composite.
The problem with the entire scenario in the
first place is that, when people die, the tissues accumulate damage rapidly as they cease to function. It's for this reason that reanimating a whole, intact corpse is nearly impossible: there's no such thing, really. There's going to me massive tissue damage over time, and quickly.
If the purpose of the composite-corpse is to negate specific instances of tissue damage (read: organ transplants, etc.) due to specifically damaged areas or causes of death (liver failure, heart failure, etc.), you may run into another problem: when the body shuts down, damage is going to occur in a relatively specific order. This is ignoring prior causes of death, and just focusing on the effects of death itself.
Thus, you're going to find pretty common damage in common areas from all deceased donors, unless you act very quickly...and with so many composite donors, the damage is going to win out. The nerve damage alone would be phenomenally difficult to repair in a composite.
Then there's the tissue rejection...I won't even go there. That one should be blatantly obvious.
I can only think of two scenarios that would make this possible:
1) Cryogenics become so advanced that we can preserve bodies and parts for
very extended periods of time,
OR
2) Stem Cell use becomes so advanced that we're able to repair/regenerate damaged tissues relatively quickly...then again, this would completely negate the need for a composite being.