Death Egg mk.II Zone

Death Egg mk.II Zone is the fifth and final zone of Sonic The Hedgehog 4: Episode II, as well as the tenth and currently final zone of Sonic 4. It is a newly rebuilt Death Egg, constructed around Little Planet.

It has constantly changing gravity, much like its predecessor. It consists of one act and a boss. This marks last place in game, where Sonic and Tails encounter Metal Sonic for the last time and have their final battle with Dr. Eggman.

Background
The Death Egg casts a shadow throughout the entire story of Sonic the Hedgehog 4. Though a similar space station appears as the final location of Episode I, the true Death Egg makes a comeback in the later half of Sonic the Hedgehog 4: Episode II as the Death Egg mk.II. This new Death Egg appears as a mechanized version of Little Planet -- Literally, the entire station is built around it! While it retains many characteristics of its predecessor, the Death Egg mk.II is still under construction and still very much incomplete. It can be seen in the Act 3's night background of Sylvania Castle Zone as well as White Park Zone. The Death Egg mk.II is shown to have a fleet of smaller, mass-produced stations which resemble the E.G.G. Station Zone.

After beating Metal Sonic in Sky Fortress Zone, Eggman ditches his damaged airship and decides to retreat to his new space station with Metal Sonic while Sonic and Tails following them in an escape pod. Inside Death Egg mk.II Sonic once again races his doppleganger only this time with Tails by his side. The duo then confronts Robotnik in the heart of the Death Egg, facing his latest creation. Upon being defeated, the new Death Egg begins to suffer massive internal damage and can be seen shutting down in space. Luckily, Sonic and Tails manage to escape at the last moment crashing down to Earth in the doctor's escape pods.

Acts

 * Act 1 - A Duel with Metal Sonic: Sonic and Tails fight Metal Sonic twice in this zone. The first time is similar to the battle with him in White Park Zone, with Dr. Eggman accompanying the robotic hedgehog. The Second is a re-make of the Stardust Speedway Race.
 * Boss - The Beginning of the End: Sonic and Tails take on Dr. Eggman's final trump card, the Egg Heart - a heart shaped machine surrounded by rotating ring shaped platforms.

Archie comics
The Death Egg Mark 2 debuted in the Archie continuity nearly a year before the games. Though similar, the Archie version differs in size and shape, and was not constructed around the Little Planet.

In this incarnation it can manipulate time and space using a Chaos Emerald, and, like its comic predecessor, is equipped with a World Roboticizer.

The Death Egg Mark 2 is Doctor Eggman's main base and ultimate weapon, originally desguised as an egg-shaped bunker. When the station attacked the Freedom Fighters base, Sonic boarded it and fought against an upgraded Silver Sonic, and another rebuilt Metal Sonic. The Death Egg later retreats after sustaining damage, but not before launching Titan Metal Sonic and Tails Doll into New Mobotropolis. (StH: #224, #225, #230, #231)

Trivia

 * While this Death Egg has constantly changing gravity similar to Sonic & Knuckles Death Egg Zone, there are no enemies present aside from Dr. Eggman and a robotic doppelganger of Sonic (in this case, Metal Sonic), making it highly reminiscent of Sonic the Hedgehog 2s Death Egg Zone.
 * In the final showdown with Metal Sonic, not only is the race from Stardust Speedway recreated, but the Stardust Speedway Bad Future music from the Japanese/European soundtrack for Sonic CD has been remixed. Metal Sonic is even defeated the exact same way as he was in Sonic CD.
 * Unlike its predecessor, which was made entirely from scratch, this Death Egg is built around the Little Planet from Sonic CD, which is also a giant spherical structure in bad future.
 * This version of the Death Egg is called "mk.II", even though there was already a Death Egg II which Dr. Eggman built in Sonic the Fighters. This could be due to the former originating from a seperate construction plan, while this station was modeled more after the original.
 * The final boss appears to look like a realistic heart, possibly because it is in the "heart" of the Death Egg mk.II.
 * Unlike its predecessor, this Death Egg doesn't plummet back down to Sonic's world or explode after the final battle. Instead, it remains stationary in orbit and all the lights on the exterior turn off, implying that while its still intact on the outside, the damages made on the inside by Sonic and Tails have caused it to power down for the time being.
 * It's also unknown if the Little Planet is saved, or if it would appear in a possible Episode 3 which contained a "To be Continued..." message in the beta files of beta 8 of Episode 2 that explains there might be a third episode.