Shelleton

Shelletons slowly walk towards the player, alternating between two modes of attack: Shelletons will collapse upon death into a skull that will be revived after a short period of time if the player fails to finish them.
 * Two wide waves of bullets centered on the player that cover about 120°. They do this attack three times.
 * A sweeping eye beam, announced by a brief red laser. The laser also damages enemies.

Trivia

 * "Shelleton" is a portmanteau of "Shell" (A bullet casing) and "Skeleton".
 * Shelletons can be spawned by Ammomancers. They immediately collapse into a skull when the Ammomancer is killed.
 * The fact that they collapse into a skull and rise again later is a reference to Mario’s Dry Bones.
 * This may also be a reference to Stalfos from the Legend of Zelda series, who collapse into a skull that must be killed to finish them off.