One more dysfunction (I don't sure if it was mentioned earlier): [vile] feats Deformity (Gaunt) and Deformity (Obese) - nothing in the prerequisites prevent skeletal creature (Undead or Construct) from taking one of those
The problem there is: the "... can be slain only by ..." line is blatantly false (for example, Regeneration can't save from lack of air - and Tarrasque's Regeneration is no different there), and enforcing regardless would make it even more silly than it already is
In the case of Sphere of Annihilation - I think it just destroys so completely there is nothing to regenerate from