The Green Hill Zone has gone mechanical, and the skies are gray with pollution thanks to Dr. Robotnik. Don't let yourself sink into the sludge in the river or you won't get out. The coconuts in the trees are explosive, so if one drops near you, get out of the way!
— Description from the Master System manual.
Mecha Green Hill Zone (メカグリーンヒル Mekagurīnhiru?, lit. "Mecha Green Hill") is the fourth Zone of Sonic Chaos for the Master System and Game Gear, coming after Sleeping Egg Zone and preceding Aqua Planet Zone. The Zone is a mechanized Green Hill Zone, which was introduced in Sonic the Hedgehog. In keeping with the other Zones of this game, Mecha Green Hill Zone consists of two standard Acts followed by a shorter, third Act which contains the boss.
Mecha Green Hill Zone is a tropical area, but everything from the ground to the trees is completely mechanized. Steel palm trees deploy explosive Coconut-Bots, and Boing-o-Bot Badniks trundle across bleak fields of synthetic grass. The ground is stark and metallic, and the skies are sickly, polluted green (or orange, on the Game Gear version). The level also incorporates the 'tilting bridges' from Gigalopolis Zone, that the player has to sprint across fast or fall off.
Mecha Green Hill Zone's boss appears to be a cross between a beetle, a sloth and a monkey. While shimmying up and down a robotic palm, the machine spits out energy bolts from a cannon hidden inside its back. Not nearly as problematic as its Sleeping Egg predecessor, the boss can be defeated through the standard tactic of dodging the attacks and jumping on its head. Another means of defeating it is for the player to jump above his head and stay there giving him repeated damage. This only works with Sonic because Tails just keeps bouncing around.
- Both the Master System and Japanese Game Gear manuals state that this Zone used to be Green Hill Zone, but for unknown reasons, this was removed from the version for the English Game Gear.
- The music in this Zone is a remix of Green Hills Zone's music from Sonic the Hedgehog 2. "Sonic - You Can Do Anything," the main theme of the Japanese/Europe version of Sonic the Hedgehog CD, uses the music as well. A faster variation is also used as the Invincibility music for Sonic Drift. Coincidentally, both Zones are based on Green Hill Zone from Sonic the Hedgehog and both are the fourth Zone of their respective games.
- Sonic Chaos page at The GHZ