Creates a large red aura around herself, then begins to fire rings of bullets which have openings in Isaac's direction. These bullets split when they exit the aura.
Sings, charming your familiars and turning them against you. You can cancel this by attacking them.
Fires music notes in random directions, which at first travel in a straight line away from her, but then begin to curve ether to the left or right.
Notes
Her ability to charm your familiars can be a real annoyance if you've got the Dead Cat, because if you kill her while she controls it she'll revive with full health, stealing one life of the dead cat in the process.
After the battle is over, The Siren's skull will lie on the floor. Breaking the skull will unlock the Song of the Siren.
Gallery
Trivia
Sirens are monsters found mostly in Greek mythology, and are usually portrayed as women with the bodies of birds. They would roost near shallow rocks and sing their hypnotizing song, trying to lure sailors to their doom.
Her "ring" attack in which tears emit from her and split once far away is almost identical to that of the Gorgun's, a boss from the game Enter the Gungeon.