SRD:Horn of Fog
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Horn of Fog: This small bugle allows its possessor to blow forth a thick cloud of heavy fog similar to that of an obscuring mist spell. The fog covers a 10-foot square next to the horn blower each round that the user continues to blow the horn; fog clouds travel 10 feet each round in a straight line from the emanation point unless blocked by something substantial such as a wall. The device makes a deep, foghorn-like noise, with the note dropping abruptly to a lower register at the end of each blast. The fog dissipates after 3 minutes. A moderate wind (11+ mph) disperses the fog in 4 rounds; a strong wind (21+ mph) disperses the fog in 1 round.