Good edits have really helped this one I think, and potentially saved it, one part tripped my 'logical fallacy' button though;
"Though the subject does not exhibit resistance to injury or death beyond the limits of a normal human, twelve (12) hours after SCP-781's physical "death" any remains of its corpse disappear. Another twelve (12) hours later, a fully healthy SCP-781 appears close to the place with the largest concentration of its remains."
How can it appear next to the place of the largest concentration of it's remains, if those remains disappeared 12 hours earlier? Maybe he reappears within X meters of this place of his death instead, maybe randomizing the distance, though that distance remains within the range of his cell.