A party was recently exploring an old, abandoned library. They triggered the emergence of several Dust Mephits, and a young wizard responded by casting Fog Cloud. As the DM, I was faced with three options:
Strict Interpretation - Since water is not listed as a vulnerability for Dust Mephits, the spell has no effect aside from the inconvenience of visual obscurance.
Moderate Interpretation - The fog cloud has the obscurance effect, and also suppresses the dust generated from the death burst of the mephits
Liberal Interpretation - The fog cloud suppresses the mephits themselves, and they simply cease to be.
Generally speaking, this falls into a set of DM calls that are outside the rules of any of the guides, but should obey the notional laws of physics that the players are comfortable with (or they will have little reference upon which to make creative decisions). Is there any guidance available that ameliorates the Strict interpretation to require that the properties listed for the spell and the creature to align with natural intuition regarding the physical world?
NOTE: What happened in the actual game was a screaming match. I liked the use of the spell (particularly by the young player) and decided to reward him with a liberal interpretation of the rule (based on my many years of living with both dust and water). The other players reacted badly, claiming that I wasn't following the rules. I've never had a party complain that monsters were defeated before...