Um, I would think a green cloud that melts everything organic it contacts would be more than sufficient. You don't just want to destroy them, you want them running away in fear, right? Ask Ironraven or Blast about Chlorine Tri-Flouride, aka N-stoff.
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The ultimate result of shielding men from the effects of folly is to fill the world with fools.
-- Herbert Spencer, English Philosopher (1820-1903)