SRD:Pipes of the Sewers
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Pipes of the Sewers: These wooden pipes appear ordinary, but if the possessor learns the proper tune, he can attract 1d3 rat swarms if rats are within 400 feet. For each 50-foot distance the rats have to travel, there is a 1-round delay. The piper must continue playing until the rats appear, and when they do so, the piper must make a DC 10 Perform (wind instruments) check. Success means that they obey the piper’s telepathic commands so long as he continues to play. Failure indicates that they turn on the piper. If for any reason the piper ceases playing, the rats leave immediately. If they are called again within a day, the Perform check DC is 15.
If the rats are under the control of another creature, add the HD of the controller to the Perform check DC. Once control is assumed, another check is required each round to maintain it if the other creature is actively seeking to reassert its control.