Corrected entry: If the dehydration machine really did what it was supposed to, the leaders would not be reduced to powder, their body would still be intact, but would have no trace of liquid in their body, which would simply kill them.
Corrected entry: In the scene where Robin discovers no yacht in the picture, Batman says as you truly remarked, no one can make a sea going vessel disappear. Robin never stated that the yacht disappeared. A reporter asked Batman about the disappearing yacht at the news conference, after the shark attack, and Batman responds how can a yacht simply disappear?
Corrected entry: How do none of the world leaders notice 4 supercriminals turning the others into dehydrated dust? Even when the one from the UK is left he is still arguing.