Elephant Gun

 is a gun. It is a double-barrel shotgun that fires a cone spread of bullets and has strong knockback.

Trivia

 * So called elephant guns were very large weapons used for hunting big game during safaris, mostly in Africa. They had tremendously large bores of up to 25mm and were fired at close range, ensuring they would knock out the huge animals they were intended to stop. While the gun present in the game fires a spread, elephant guns loaded single lead projectiles, but they could be rifled or smoothbore.
 * Piano keys used to be made from elephant tusk ivory, hence "pianos out of teeth".
 * "An inelegant weapon for a less civilized age" is a reference to Star Wars, where the reverse of the phrase is used to describe a lightsaber.
 * The gun could also be a reference to Looney Tunes and Elmer Fudd, the hunter who chases Bugs Bunny and uses a similar two-barreled shotgun. The lines "shoots elephants" and "used to make pianos out of teeth" are referencing gags which occur in several episodes.
 * The fact the gun fires two shots could be a reference to George Orwell's 1936 essay "Shooting an Elephant" in which the narrator recounts shooting an elephant multiple times.
 * The Elephant In The Room synergy's special bullets' appearance may be a reference to Phan Phan, a recurring enemy in the Kirby series.