3D graphics were created using the Nichimen N-World toolkit running on a Silicon Graphics workstation. The team placed high priority on Mario's movement and, before levels were created, they tested and refined Mario's animations on a simple grid. The first test scenario for controls and physics involved Mario interacting with a golden rabbit, named "MIPS" after the Nintendo 64's MIPS architecture processors; the rabbit was included in the final game. The developers tried to a multiplayer cooperative mode, whereby players would control Mario and his brother Luigi in split-screen, but could not make it work satisfactorily. To assist players with depth perception, the team positioned a faux shadow directly beneath each object regardless of the area's lighting. Assistant director Yoshiaki Koizumi described the feature as an "iron-clad necessity" which "might not be realistic, but it's much easier to play."