Sonic the Hedgehog Chaos

"Amazingly, the universe began in chaos. Things were fast, it was cool. Over the years, that chaos would take many forms, but one thing it's never become is portable!"

Released towards the end of 1993 for the Sega Game Gear and Master System, Sonic Chaos--or Sonic & Tails as it's called in Japan--makes quite a few improvements upon its predecessor, the 8-Bit version of Sonic the Hedgehog 2.

South Island is in turmoil. In his latest scheme to Take Over the World, Dr. Robotnik has just nabbed one of the seven Chaos Emeralds, and as a result, South Island is on the verge of sinking into the ocean. Getting wind of this scheme, Sonic and his buddy Tails must retrieve the other six Emeralds and steal the seventh back from Robotnik before it's too late. With six zones, three acts each, and six Emeralds to collect, it's time to hero up and save South Island!

Sonic Chaos presents a couple of firsts for 8-Bit Sonic. Notably, it's the first where the Chaos Emeralds are collected via Special Stage instead of in the actual zones, the first to feature the Spindash, and also the first to allow you to play as Tails.

But in a first for the series as a whole, Sonic and Tails were differentiated gameplay-wise. Sonic can perform the Peelout/Strike Dash - a technique carried over from Sonic CD - and for some reason, he's the only one who can enter Special Stages (by collecting 100 Rings in a regular act). Tails is slower, but he can fly, and he has the benefit of starting the game with a couple of continues (Sonic has to work for his!). Needless to say, Tails' game is considered the easier of the two.

Items introduced here were the Rocket Shoes, which sends your character forward with a powerful thrust of speed and mild flight capabilities for a short period of time, and the Pogo Spring, which allows you to do extra high jumps but also for a short period of time.

Tropes used in Sonic the Hedgehog Chaos include:

Acrofatic: Eggman managed to keep pace with Sonic in the bad ending.
Eternal Engine: Electric Egg Zone.
Green Hill Zone: Turquoise Hill Zone.
Hailfire Peaks: Mecha Green Hill Zone combines Green Hill Zone with Eternal Engine, resulting in a once beautiful tropical paradise industrialized in the ugliest way possible.
Law of One Hundred: How you get into the Special Stages.
Made of Explodium: The explosive coconuts in Mecha Green Hill Zone.
No Ending: Even when playing as Sonic, and clearing the game with all emeralds, all you get is a slighty different credits sequence.
Recurring Riff: Mecha Green Hill's theme is You Can Do Anything (a Jimmy Hart version, actually). It's also part of the final boss theme and invincibility theme.
Shout-Out: The level select (Up, Up, Down, Down, Right, Left, Right, Left, Start at the title screen) and sound test (Down, Down, Up, Up, Left, Right, Left, Right, 1, 2, Start at the title screen) codes are both variations on the Konami Code.
- In the sound test menu, if you perform a code, Sonic will pull off a Hadouken.
Tomorrowland: Gigapolis Zone.
Underwater Ruins: Aqua Planet Zone, which contrary to its name, is still on South Island, and thus still on Earth/Mobius/whatever.