Cubus Sisters

The Diabolical Cubus Sisters are the fourth boss in Phantom Hourglass. They are fought on top of the Ghost Ship.

Throughout the dungeon, Link rescues four sisters from the ship, eventually reuniting all of them. They agree to thank Link, and bring him to the top of the ship, where they reveal themselves to be ghostly monsters: the Four Cubus Sisters.

Strategy
Three will shoot laser beams down at Link, while the other will send down an energy ball. In a game of Dead Man's Volley reminiscient of Phantom Ganon, Link must hit the energy ball back at the Cubus Sister. Once the first is gone, the remaining three will hit the energy ball between themselves to disorient Link. Once only one remains, it will also send out two fake energy balls that will harm Link if he hits them. The fake ones look different from the real energy ball, so Link will be able the see the real energy ball easily. Once defeated, a Heart Container is obtained, and Link gains a key to a secret room of the Ghost Ship.

Trivia

 * The Cubus Sisters' name references the Poe Sisters of Ocarina of Time, who share a Poe-like appearance, relativity, and four siblings with their precendents.
 * The Cubus Sisters strongly resemble the Poes seen in The Wind Waker, especially their multi-colored cloaks and masks. It's possible that they are Poes, though they lack lanterns.
 * The name "Cubus" may branch off of the last five letters of the word "Succubus", which refers to a female demon which seduces men in order to steal their life force.
 * When talking to the third Cubus Sister about the two treasure chests in the basement of the Ghost Ship, she will ask Link if he knows his left and right. If he says no, she will say that the left is the one that is not right. When she says "left", it is in bold text, "right" is not, an indication that the right chest is the correct choice.