Grab a Hop Spring and bounce through mazes of blocks. Break paths to monitors and secret passageways. Looks can be deceiving, and platforms that appear solid might not be. One wrong step, and it's a long way down!
— Description from the Master System manual.
Sleeping Egg Zone (スリーピングエツグ Surīpinguetsugu?, lit. "Sleeping Egg") is the third Zone of Sonic Chaos for the Master System and Game Gear. In keeping with the other stages of this game, Sleeping Egg consists of two standard Acts followed by a shorter, third Act which contains the boss.
Sleeping Egg Zone is an unusual stage with many breakable blocks, and numerous foreground walls emblazoned with Robotnik's image (as in Crystal Egg Zone for Sonic the Hedgehog 2 (8-bit)). There are industrial-strength pogo springs scattered throughout the level, which our heroes can use for bouncing up to otherwise inaccessible areas.
The greatest danger in Sleeping Egg Zone comes not from the Badniks or other hazards, but rather falling off the screen in one of the many yawning, bottomless voids that litter the stage. It seems the best way to classify Sleeping Egg is as some sort of high-altitude construction site of Robotnik's; as some of the level appears incomplete, with metal frameworks and half-finished blocky walls.
Sleeping Egg Zone's boss is (in keeping with the pogo spring theme of the level) a bouncing, gun-toting, Robotnik-look-a-like robot. This machine can actually provide some problems, as only the head is vulnerable, and the speed of its bouncing is such that landing a strike takes some work. All the while, the boss' cannon spits bullets in Sonic or Tails's direction.