User blog comment:Yatanogarasu/What Did Blackbeard Do to Get the Gura Gura no Mi?/@comment-1595565-20101231210311/@comment-174.254.154.215-20121225131845

His logia fruit already gives him the immunity to damage like other logias. The difference for Blackbeard is that his fruit absorbs EVERYTHING including pain, so even if he can't be damage by normal moves (he should still be affected by haki and presumably some sort of anti-dark attack) he still feels the pain, even more so than a normal person.

Let me give you an example. Let's say someone stabbed Teach with a knife. Even though he would feel a sharp pain, and it would hurt him more than it would a normal person, he would not be left with a stab wound. It would just be super painful for him. This absorption principle is the same for any damage that a logia user might normally receive.