The Famicom’s Built-In Microphone Was Wonderfully Weird kotaku.com

Added by Nintendo research and development head Masayuki Uemura, the second player microphone was hardly the console’s main draw.
In the game, Pols Voice are depicted as ghostly rodents with enormous ears, usually found scurrying about dungeons in packs of three to five.
With a mighty roar into the second player microphone, adventurers could eradicate any Pols Voice on screen.
This method was much preferred to attacking with normal weapons, as each Pols Voice took multiple hits to defeat.
In the commercials Takeshi can be seen yelling into the Famicom microphone to bring up a map, as well as singing a snippet of karaoke to raise his spirits.