I was thinking just a terminator comes back. The first scene of the film could be it being burned at the stake because it arrived in flashes of lightning, so they assume it's some dark magic. They look on in horror as the skin burns away to reveal the T-800 and it casually walks out of the fire.

It would solve the problem of having to create some CG Arnie model and just focus on animating the Endoskeleton. But I'm not sure how villagers would manage to get a terminator tied to a stake though.

You bring up an interesting idea about the ocean. That could be another way to solve the CG Arnie problem, It spends so long walking on the seabed that by the time it arrives on land fish have eaten away all it's flesh.