Tribute 1 face-up monster; Special Summon from your Deck, 1 monster with the same original Type and Attribute, that the Tributed monster had on the field but 1 Level lower. You can only activate 1 "Downbeat" per turn.
You can use Swamp Mirrorer to select any Type of Attribute and it becomes those properties, then you can use Downbeat to bring out any monster that is 1 level lower than Swamp Mirrorer but has the same Type and Attribute that you declared. You can use Downbeat on Meitiel, Sage of the Sky, Zeradias, Herald of Heaven, Harvest Angel of Wisdom, or Bountiful Artemis, in order to Special Summon The Agent of Creation - Venus from your Deck. The Agent of Creation - Venus is able to subsequently Special Summon Mystical Shine Ball from your Hand or Deck by paying 500 Life Points.