Shoot em up (also known as shmup) is a sub genre of shooter video games. In a shoot em up, the player controls a lone character, often in a spacecraft or aircraft, shooting large numbers of enemies while dodging their attacks. The genre in turn encompasses various types or sub genres and critics differ on exactly what design elements constitute a shoot em up. Some restrict the definition to games featuring spacecraft and certain types of character movement; others allow a broader definition including characters on foot and a variety of perspectives. Shoot em ups call for fast reactions and for the player to memorize levels and enemy attack patterns.Newer bullet hell games feature overwhelming numbers of enemy projectiles, the patterns of which the player must memorize in order to avoid.