Cyclonemon

The Dark Whirlpool, as noted by the  Digimon Emperor, was created by the presence of an evil  Digimon. The Emperor brought his fortress inside the Whirlpool, but was pursued by T.K. ,  Pegasusmon  and  Tentomon. Wraith-like images swirled in the air around them, and Pegasusmon told T.K. not fear, although he and the other Digimon nearby, including Wormmon, could feel an evil presence within the pool. Venturing inside the Whirlpool in a  Mekanorimon, the Emperor confronted the presence in question -  Devimon ! Devimon told the Emperor to beware the darkness, but he paid no heed, and harvested some of Devimon's data for use in the creation of  Kimeramon. Later encounters with the same feeling and energy that the kids experienced within the pool makes it clear that the Dark Whirlpool was some form of gateway into the  World of Darkness  - it was most likely only temporary, to lure the Emperor in to attempt to prevent him from his plans to control the forces of darkness. The Dark Whirlpool appears in "An Old Enemy Returns."