Gotcha. If you fix the first sentence on killing touch to separate the action on living opponents from dead ones, it would be a lot clearer. It also helps if you list all the requirements first such as needing less than zero hit points, breathing air and containing water. Plus, if this is the only way they gain sustenance, it makes them a bit creepier.

Some creatures can continue fighting without penalty while dying like dire boars. Shouldn't they have save even if normally there isn't one?

Since dying creatures are normally unconscious, does it matter if the previous attack is successful or not?

Debby