tar is in old saves in unexplored areas. same for anything else new like seeds...

the serpent glow and are bigger than a longship and aggro you from quite some distance. Can't miss em at any speed, even if you want to!

you can regenerate your map seed (that is, restart that seed from scratch) but not areas. You can fix damage, like fill in a hole and grass it over, but its never quite like it was.