Sonic the Hedgehog 4: Episode II
After Metal Sonic's defeat in Sky Fortress Zone, Eggman abandons the airship and flees to his new space station alongside Metal Sonic. To escape the Sky Fortress, Sonic and Tails decide to use an escape pod, which follows Eggman and Metal Sonic to the Death Egg mk.II, where Sonic once again races his doppelganger with Tails by his side this time. The fight is an obstacle course to the end, just like Stardust Speedway's battle in Sonic the Hedgehog CD; after besting Metal Sonic in the race, he is defeated once again.
The duo then confronts Eggman in the heart of the Death Egg, facing his latest creation, the Egg Heart, it attacks by spinning the platforms you are standing on and electrifying them. 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 leaving the new Death Egg shut down, still built over the Little Planet.
Act 1 - A Duel with Metal Sonic
As seen in levels of previous Sonic the Hedgehog games that take place in space, gravity will constantly change at various points throughout the Zone. Unique to this game though, the player's Up and Down inputs on have been inversed while up-side down (although horizontal movement remains unaffected). 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 race similar to Stardust Speedway Zone 3 in Sonic CD.
Boss - The Beginning of the End
Sonic and Tails take on Dr. Eggman's final trump card, the Egg Heart - a machine shaped like a human heart surrounded by rotating ring shaped platforms.
- While this Death Egg has constantly changing gravity similar to Death Egg Zone in Sonic & Knuckles, 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 'Death Egg Zone in Sonic the Hedgehog 2.
- In the final showdown with Metal Sonic, not only is the race from Stardust Speedway recreated, but the Bad Future music from the Japanese/European soundtrack for Sonic the Hedgehog CD has been remixed. Metal Sonic is even defeated the exact same way as he was in Sonic the Hedgehog CD.
- Unlike its predecessor, which was made entirely from scratch, this Death Egg is built around the Little Planet from Sonic the Hedgehog CD, which is also a giant spherical structure surrounding Little Planet.
- 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 it's 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 is also unknown if the Little Planet is saved, or if it can disappear from inside the Death Egg.
- During the mid-boss with Metal Sonic, the version of Stardust Speedway's theme played is the second remix of the tune, as the song is essentially a remix of a remix, based on Sonic Generations' version.
- This version uses some of Sonic 3's soundfont, such as the "80's drumming" synth in the background, but also uses the one from Sonic 2 as well, making it sound like a hybrid mix of the Sonic 3 and Sonic 2 soundfonts in the form of Stardust Speedway's bad future theme. Note that it still bears the signature "Sonic 4 Dying Cat" noises in a lower pitch.
- The escape pods' design is similar to the Bridge Zone boss from Sonic the Hedgehog (8-bit).
- The design of the Death Egg Mk.II level and background is inspired by Dead Line from Sonic Rush.
- The race with Metal Sonic is the only boss in Sonic the Hedgehog 4: Episode II to be reused from a previous game.