From Sonic Retro
The Showdown is the fourth and final level of Sonic Spinball for the Sega Mega Drive, coming after The Machine. As with other stages in this game, Sonic must bounce through the pinball-like level, acquiring Chaos Emeralds which are in turn used to access the boss, Robotnik's Ship. In this stage, there are 5 gems to find.
After Sonic destroyed the Veg-O-Machine in the previous stage, Eggman detatched his self-imaged spacecraft from the launch base at the top of Mt. Mobius, attempting to escape to the stars. Showdown takes place both in the sunset scaffolding of the rocket's launch pad, and inside the hovering starship itself. At the bottom of the level rests the magma-filled caldera of the mountain; missing the flippers means instant, fiery death.
Instruction Manual Description
The Veg-O-Fortress is caving in on itself! Grab the last Chaos Emeralds and fight toward Robotnik's escaping rocket ship.
You'll face a treacherous climb through the space hangar. Krondors block your way and Robotnik's cockpit is armed and dangerous!