Peregrine Drake | Cavern Harpy | Panharmonicon

Cards

You control up to five lands that can tap to produce at least ({2} magic symbol) ({U} magic symbol) ({B} magic symbol) .

Activate up to five lands you control by tapping them, adding at least ({2} magic symbol) ({U} magic symbol) ({B} magic symbol) .
Cast
Peregrine Drake by paying ({4} magic symbol) ({U} magic symbol) .
Peregrine Drake enters the battlefield, triggering its ability twice.
Resolve the first
Peregrine Drake trigger, untapping the five lands.
Activate the five lands by tapping them, adding at least ({2} magic symbol) ({U} magic symbol) ({B} magic symbol) .
Resolve the second
Peregrine Drake trigger, untapping the five lands.
Cast
Cavern Harpy by paying ({U} magic symbol) ({B} magic symbol) .
Cavern Harpy enters the battlefield, triggering its ability twice, returning
Cavern Harpy and
Peregrine Drake from the battlefield to your hand.
Repeat.