Theme Deck

Very often in anime, the characters who have a great deal of expertise and a huge library of attacks rarely use all of them. As a matter of fact, they will only use a select few.

This is usually a Justified Trope, as it wouldn't make for much Character Development if a character was able to pull a new attack out of their hat every episode. Further, it makes sense that a veteran fighter would use the moves that he knows work, instead of trying a risky new strategy that could easily backfire. But still, when you hear the Combat Commentator explain that this character has an insane library of powerful attacks, you can't help but wonder... Most often than not, it's purposely done to make for easy Asspulls later on down the line.

Compare to Poor Predictable Rock. See also its Professional Wrestling equivalent, Five Moves of Doom.

Anime and Manga

 * In Naruto, Sasuke has an ability that enables copying powers by looking at them. Instead of actually using any of the abilities he sees someone else using (with the exception of one hand-to-hand combat combination), he uses derivatives of two attacks he learned normally (Great Fireball and Chidori), said ability's other powers, and.
 * Even more specific to this trope, is Sasuke's original teacher, Hatake Kakashi, who also has the Sharingan that allows copying. Kakashi however has been in combat with it for seventeen years when the series began longer than Sasuke's been alive, and despite not being a member of the family known for having the ability, has built a world renowned reputation as "The Man who has copied One Thousand Technique, Copy Ninja Kakashi". Counting the six anime additions, he has shown 29.
 * Inuyasha and his teammates only have a handful of attacks, and they're all really powerful.
 * Miroku occasionally shows the ability to use sutra magic techniques to do some neat things. But 95% of the time he just either hits things with his staff or whips out his wind tunnel, which is a little jarring since you'd think he'd try magic before the wind tunnel since he's risking suicide every time he uses it.
 * Magical Girl Lyrical Nanoha and her friends' magical libraries are never mentioned, but they nonetheless tend to use abilities with a theme, such as Nanoha's Divine Shooter... though on several occasions where it's not appropriate, she just switches to something else without a comment (or with a 'just what we expect of'), such as suddenly turning her Device into a spear to break through a shield before unleashing an uber-pink-laser-of-death at point blank range.
 * Ranma in Ranma ½ has, by the time Bit Villains Rouge and Pantyhose are battling over his home, an impressive array of deadly combat techniques such as ki blasts, invisibility, and the ability to create tornadoes. But he uses none of them, despite the fact a giant monster and a demon-goddess are wrecking the neighborhood. Secret techniques are usually used only in the story arcs they are learned in, when they'll be useless to the good guys, or in the Final Story Arc. He usually relies on his other skills and the Saotome Secret Technique (Run Away! Run Away!), which provides dramatic tension and the possibility of failure.
 * Inverted in Bobobo-Bo Bo-bobo, where the title character actually goes out of his way to avoid reusing moves; pointed out in the one episode he does reuse one.
 * When your fighting style is confusing your opponent into submission, reusing moves isn't recommended. Or funny.
 * For the record, he and  have the specific theme decks of using various forms of body hair. How they can get creative with that is quite stunning.
 * In Bleach Aaroniero Arruruerie tells Rukia he can use the powers of all 33,650 hollows he's eaten all at once. He proceeds to use the same technique he had been using, and is stabbed through the head by Rukia fairly quickly. While he was enjoying his mind games employed through what he had been using, he definitely could've been more careful.
 * Slightly subverted by one of the villains in Yu Yu Hakusho. Rando, the demon from the Genkai Tournament arc, is known for having killed and stolen the secret techniques of over a hundred psychics, and throughout the battle he pulls out move after move. And then loses when one of them backfires on him, because despite knowing how to perform the techniques, his understanding of them is limited and what he didn't know damn near did kill him.
 * And then really subverted in the Dark Tournament arc, when self-described "Beautiful" Suzuka revealed that not only did he have a vast arsenal of techniques, he was extremely well versed in using them. Unfortunately for him, he was sorely lacking in raw power, which Genkai made painfully clear by beating him into the ground.
 * Averted in A Certain Magical Index II with Oriana: she never reuses attacks since she thinks using a spell she already used in the same fight is boring.

Collectible Card Games

 * This is actually very common in collectible card games. And justified, because by the rules of most of said games, not playing a theme means you'll have a handful of unrelated and usually unplayable cards.
 * Take the Pokémon TCG as an example. Pokémon require energy for their attacks. You'll have a much easier time providing your Pokémon with energy if you focus on a single (or sometimes two) type(s). Fire Energy isn't really going to help you if you if you don't have any Fire Pokémon in play/your hand. Similarly, Pokémon that require multiple types of energy for their attacks aren't that useful.
 * A similar thing happens in the Yu-Gi-Oh! card game. Archetypes are made, and while this isn't necessarily a bad thing, some outright suck, while others have enough support to build several normal sized decks without repeats.
 * Furthermore, if a powerful combo is found by combining things that usually aren't used outside of theme decks, they'll BAN the cards altogether.
 * This happens in Magic the Gathering too. For instance, the Scars of Mirrodin block introduced the concept of infect and proliferate. Creatures with infect do damage to players in the form of poison counters (If you get ten, you lose the game, and only one ancient card can get rid of them, and back then, poison wasn't really a threat.), and to creatures in the form of permanently weakening them with other counters. When you proliferate, you add one counter of a type already on that card or player to each card or player you choose to. However, infect damage does not cause loss of life, so most of the time you're not doing much at all if you combine infect creatures with non-infect creatures in a deck.

Comic Books

 * A common criticism of Green Lanterns is that each has a ring that can, canonically, do "anything its wearer can imagine"; the more abstract applications tend to be downplayed in favor of energy blasts, force fields, etc.
 * Although the infamous All Star Batman and Robin did show his using a coathanger.
 * Specifically addressed in an episode of Justice League, where GL instructor Katma Tui criticizes her trainees (and John Stewart in specific) for not getting creative with their rings. Since John's an ex-Marine, one can understand his preferring function over form; however, after this episode (and one where he's de-aged to childhood) he does start showing some creativity. This doubles as a meta example, since fans of JL had also complained about Stewart only using "beams and bubbles" in early episodes.

Live Action TV

 * Main antagonist Sylar on Heroes has a variety of stolen superpowers (including freezing, liquifying solid objects, and nuclear energy blasts), but he almost exclusively uses telekinesis for combat.

Video Games

 * Between the Five Moves of Doom nature of early Final Fantasy magic, the fact that Black and White Magic used two different stats, and the fact that in Final Fantasy II, spells (and stats) grew in strength with number of times used, this was encouraged.

Real Life

 * Martial arts themselves are to an extent theme decks.
 * Many national-or-higher level judoka, possibly all of them, specialize in a maximum of five throws and grapples, in spite of knowing nearly every technique of their chosen martial art.
 * Even high-ranked tai kwon do competitors have kicks and blocks that they prefer, usually depending on their size and flexibility.
 * Even the bafflingly extensive Kung Fu styles like Shaolinquan encourage the development of one or two specialized skills. The best known of these is likely the Iron Palm skill.