Comedy as a Weapon

Instead of sheer force, a BFG or a great display of magic, a character uses jokes, puns, slapstick, laughs, etc... to fight an enemy or achieve a goal.

Anime and Manga

 * In the Pokémon anime, Ash's Haunter saves the day by making Sabrina laugh with its antics.
 * Bobobo-Bo Bo-bobo is nothing but Comedy as a Weapon -- in-universe, it's an actual fighting style known as Hajike ("Wiggin" in English) used by most of the main characters. It mostly consists of unpredictable attacks, sight gags, and puns used to confuse or drive their opponents (and sometimes their allies) crazy.

Film

 * In Who Framed Roger Rabbit?, Eddie.
 * In Patch Adams, the titular character believes in helping patients through humour and laughter.
 * Assuming the 'etc' above includes music, the way The Beatles fight the Blue Meanies in Yellow Submarine.

Literature

 * In Stephen King's Wizard And Glass, Eddie kills Blaine the Mono by telling him a lot of lame jokes.
 * They are not just lame jokes, they have no logic, no smart puns. He basically kills Blaine with non-sequiturs.
 * tries this with Roland in the final book.

Live Action TV

 * The "World's Funniest Joke" sketch from Monty Python's Flying Circus.
 * In the "Piranha Brothers" documentary, Doug Piranha kept his underlings in fear by his use of sarcasm. He knew all the tricks - dramatic irony, metaphor, bathos, puns, parody, litotes and...satire. Grown men would pull their own heads off rather than see Doug.

Video Games

 * The results of sword fights in the Monkey Island games are based entirely on insults and puns.

Webcomics

 * In 8-Bit Theater Black Mage kills using bad puns.
 * In The Order of the Stick, Elan's moves as a Dashing Swordman gain more power if he tells a pun while attacking. The worse the pun, the greater the damage.