added cover mechanics to the formula, and Data East's RoboCop (1988). In 1987, Konami created Contra, a side-scrolling coin-op arcade game, and later a NES game, that was particularly acclaimed for its multi-directional aiming and two-player cooperative gameplay. By the early 1990s and the popularity of 16-bit consoles, the scrolling shooter genre was overcrowded, with developers struggling to make their games stand out, with exceptions such as the inventive Gunstar Heroes (1993) by Treasure. Sega's pseudo-3D rail shooter Buck Rogers: Planet of Zoom demonstrated the potential of 3D shoot 'em up gameplay in 1982. Sega's Space Harrier, a rail shooter released in 1985, broke new ground graphically and its wide variety of settings across multiple levels gave players more to aim for than high scores. In 1986, Arsys Software released WiBArm, a shooter that switched between a 2D side-scrolling view in outdoor areas to a fully 3D polygonal third-person perspective inside buildings, while bosses were fought in an arena-style 2D battle, with the game featuring a variety of weapons and equipment. In 1987, Square's 3-D WorldRunner was an early stereoscopic 3-D shooter played from a third-person perspective, followed later that year by its sequel JJ, and the following year by Space Harrier 3-D which used the SegaScope 3-D shutter glasses. That same year, Sega's Thunder Blade switched between both a top-down view and a third-person view, and featured the use of force feedback, where the joystick vibrates. Bullet hell and niche appeal (mid-1990s to present) Over the course of the 1990s, a new subgenre of shooters evolved, known as " in Japan, and often referred to as "bullet hell" or "manic shooters" in English-speaking regions. These games are characterized by high numbers of enemy projectiles, often in complex "curtain fire" patterns, as well as collision boxes that are smaller than the sprites themselves, allowing the player to fit between the narrow gaps in enemy fire. Bullet hell games were first popularized in Japanese arcades during a time when 3D games and fighting games were eclipsing other games. The flashy firing patterns were intended to grab players attention. Toaplan's Batsugun (1993) is often considered a pivotal point in the development of this subgenre. After the closure of Toaplan, the following year, a number of studios formed from former Toaplan staff that would continue to develop this style, including Cave (formed by Batsugun's main creator Tsuneki Ikeda) who released 1995's seminal DonPachi,