Twinrova

Kotake and Koume, collectively known as the Twinrova Sisters are a pair of witches that feature in several Zelda games, most notably in Ocarina of Time, in which they act as the boss of the Spirit Temple. The two sisters, Koume - sorceress of flame, and Kotake - sorceress of Ice, are able to fight individually with elemental attacks or combine together into a more powerful form.

The two Gerudo witches play an important role in a few games in the Zelda series. They are both the surrogate mothers of the Gerudo King, Ganondorf, being somewhat his more devoted servants. Their specialty is brainwashing others to serve Ganondorf (most notably Nabooru) and merging to form the stronger witch "Twinrova", where their combined power is much deadlier. The brooms the sisters use to fly become scepters Twinrova performs her spells with.

Ocarina of Time
Kotake and Koume reside in the Spirit Temple and they make their first appearance when they kidnap Nabooru (the rebellious second-in-command of the Gerudos) who is the Sage of Spirit. They brainwash her, disguise her as an Iron Knuckle, and make her face Link. Link wins this battle and releases Nabooru.

Koume and Kotake fight with magic bolts of the elements they each had power over: fire and ice. Using the Mirror Shield, Link is able to redirect their attacks at each other - this part requires four hits. Once merged into Twinrova, the Mirror Shield proves essential once more in defeating them. At the end of the battle there is a humorous cutscene of the two sisters with halos over their heads rising to the heavens, oddly enough, as they argue about their ages and insist that one or the other is senile. "But I'm only 400!" "And I'm only 380!" "How can you be younger?! We're twins!"

On an interesting note, the Hylian writing on Kotake's and Koume's headbands is in fact the different, new Hylian alphabet used in The Wind Waker, and not the one used everywhere else in Ocarina of Time. The bands simply say "Kotake" and "Koume".

If Navi is consulted during the battle with Twinrova in her ultimate form, she will react with great fear, indicating that Twinrova is a legendary terror.

Majora's Mask
Koume and Kotake also exist in the parallel world of Termina, the two run the Swamp Boat Tour and the Magic Hags' Potion Shop in the Southern Swamp. Koume searches for mushrooms in the nearby Woods of Mystery, while Kotake generally stays at the shop. Koume also works as the swamp boat tour guide.

When Link enters the Woods of Mystery, Kotake is searching for Koume because she took so long to find some mushrooms. Link later finds an injured Koume, who tells him she was attacked by the Skull Kid, and asks for a Red Potion to heal her injuries. After Link gives her the potion, Koume returns to help run the swamp boat tour guide and assist Link. These versions of Koume and Kotake, being from the alternate world of Termina, are not evil like their Hylian counterparts.

Oracle of Ages and Oracle of Seasons
In Oracle of Ages and Oracle of Seasons, Koume and Kotake sent Veran and Onox to cause chaos and light two of the three flames needed to resurrect Ganon; the Flame of Sorrow and the Flame of Destruction. Once the flames were lit, the two kidnapped Zelda to light the final flame via sacrifice: the Flame of Despair. Link fought the sisters as separate entities and as Twinrova. Defeated, the two became victims of their own ritual, acting as the vessel for Ganon instead of Zelda. Unfortunately for the pair, their sacrifice was in vain, as it only allowed a mindless, raging Ganon to come forth. Thus, Link was able to defeat it and save the day.

Trivia

 * Twinrova served as a surrogate mother to Ganondorf in Ocarina of Time.
 * "Koume" is a Japanese pickled plum.
 * "Kotake" is a type of Japanese mushroom.