Xygal

The Xygal are an alien species from the Uncharted Territories.

Biology
Statuesque aliens with skin as smooth a iridescent film that covered their internal organs. When they laugh, the Xygal emit a sound that can pierce into another sentient's very being. They then oscillate and can turn into physical light to attack and kill their victims.

Source

 * Farscape: The Official Magazine, Issue 4: "Double Trouble" by Lily Taylor