Stronger Sibling

In most games, if the Big Bad has a sibling, it will be even stronger than the Big Bad itself. Mostly these appear as Bonus Bosses, but in some cases they may serve as a plot twist. This is a natural consequence of the Sorting Algorithm of Evil; if you find yourself fighting a bad guy's relative later on, that relative will necessarily be tougher in order to keep pace with your increased skills.

Not to be confused with the Cain half of Cain and Abel. Also, many of these are big spoilers, so read with caution.

See also Always Someone Better, Aloof Big Brother. You might find them Avenging the Villain.

Literature

 * Lampshaded in Harry Potter and The Chamber of Secrets when, after Dobby tells Harry that Voldemort is not responsible for the shit hitting the fan this year, a Genre Savvy Harry asks whether Voldemort's got a brother.
 * Older Than Steam: The Arabian Nights version of Aladdin has the Big Bad's brother (also an Evil Sorcerer, the vizier is more an Obstructive Bureaucrat in this one) is the villain of the second part, and far more powerful.

Manga and Anime

 * An Anti-Hero example, Nanami from Katanagatari is by leagues stronger than her brother Shichika. When she was younger, her father refused to train her in the Kyoutoryuu style, not because she was a girl, not because she was always sick, but because she's far too strong for him.
 * A Dragon Ball Z Non-Serial Movie is based on Freeza's stronger older brother Coola showing up on Earth to kill Goku for killing his brother. (Yeah, we know that was Trunks. It's a movie...)
 * Maybe Cooler merely thought Goku was the one who did it, and didn't know that it was actually Trunks who did the deed.
 * The Gorgon Sisters from Soul Eater and Soul Eater Not. Medusa, Arachne and Shaula are savvy, manipulative, experimenting, animal themed, hot witches who each held the title of the lead antagonist at different periods and otherwise act to one up each other, the good guys and even more villainous factions.

Video Games

 * in Mario & Luigi: Partners In Time.
 * Flandre Scarlet from Touhou Project's sixth game, Embodiment of Scarlet Devil (her sister, Remilia, is the game's last boss).
 * From a much earlier game, Lotus Land Story, Mugetsu is the extra stage's first boss and Gengetsu is the extra stage's second boss. Though having no last name, official material states that they are twins.
 * Shizuha Aki is the midboss to Minoriko Aki's stage in Mountain Of Faith.
 * And in Subterranean Animism, Koishi Komeiji (Extra stage) to Satori Komeiji (fourth stage).
 * Death and Schirach from Romancing SaGa. Death is the most powerful physically and controls Necromantic magic, and Schirach has the most powerful magic of the Trio of Dark Gods. However, if you power up the Big Bad to its fullest then the point is rendered moot.
 * in Paper Mario: The Thousand-Year Door actually has two other siblings.
 * is actually the Big Bad's pet, and is a lot more difficult to beat than the Big Bad is.
 * Final Fantasy XI: After defeating  halfway through the Rise of the Zilart missions, you find out that his   is really   and serves as the Final Boss at the end of the mission set.
 * Of Resident Evil's Ashford twins, Alexia is the smarter and tougher one
 * also does this with strong implications that  Check the files in chapter 6-2 and Lost in Nightmares, it's sad indeed.
 * In Mother 3,, and proves to be much stronger than your entire party.
 * Rick and Nick Bruiser in Super Punch-Out.