Under Ground Zone is the first Zone in the 8-bit version of Sonic the Hedgehog 2. As with other Zones in this game, Under Ground consists of two standard Acts followed by a shorter third Act which contains the Zone's boss.
Under Ground Zone is notable for being atypical of the series' usual tropical island trope, which is usually the setting of the first Zone. It takes place in a magma-filled rocky mine, where Sonic will ride minecarts to dodge spikes and lava traps. At the top of the Zone, the player can get a view of the craggy mountains that make up the background, and by using the Spin Attack, the player can break through certain walls to access hidden routes.
Considerably less difficult on the Master System version, the Game Gear version is notorious for its steep difficulty. The boss of this level is also infamous for its difficulty in the Game Gear port, as the limited playing field and varying speed of objects coming onscreen makes them difficult to dodge.
|Lava and needles falling from the ceiling await Sonic’s rush underground. Make good use of “hole-digging Sonic” and “High-speed Minecart” and go for it. You’ll see, it’s easy.
— Sonic the Hedgehog 2 JP Game Gear manual (translation by Vertekins)
|Hop on a runaway railcart for the ride of your life through showers of spikes and over daredevil jumps. Buzz-saw your way through to secret tunnels and hidden Monitors. Sometimes it's hard to get enough momentum for a good ground attack, but get a running start and keep trying!
— Sonic the Hedgehog 2 US Game Gear manual
|New Motora — Similar to Moto Bug. Beetle bots which simply roll back and forth in a small area.
|Meleon — Also known as Newtron. Chameleon bots which appear on walls, then transform into missiles and fire themselves on a horizontal path in Sonic's direction.
|Taraban — Similar to Crabmeat. Crab bots which quickly move back and forth over a small area. Every once in a bit they pause to fire flashing projectiles in either direction.
Chaos Emerald location
The Chaos Emerald located in this Zone is in Act 2. Towards the end, the player will find a spring with a New Motora near it. They must hop on the spring but do not turn right: go left, then roll down the ramp. If successful, a mine cart will appear. Hop in to it and jump off at a staircase. Follow the stairs to the blue Chaos Emerald.