Final Egg

Final Egg (ファイナルエッグ) is an action stage from the game Sonic Adventure and Dr. Eggman's secret base hidden deep in the jungle of the Mystic Ruins. It is played as the first stage in Gamma's storyline, and is the final stage in both Sonic's and Amy's storyline. E-102 Gamma was also created in the base.

Sonic

 * Level C - Go to the center of the base!
 * Level B - Collect 50 rings and destroy the capsule!
 * Level A - Destroy the capsule within 4 minutes 30 seconds.

Amy

 * Level C - Evade Zero and grab the balloon!
 * Level B - Collect 50 rings and grab the balloon!
 * Level A - Grab the balloon within 2 minutes 30 seconds.

E102 Gamma

 * Level C - Destroy the "Sonic Doll"!
 * Level B - Collect 50 rings and destroy the "Sonic Doll"!
 * Level A - Destroy the "Sonic Doll" with more than 150 seconds remaining!

Archie Comics
Final Egg is mentioned in the Archie Comics' Sonic the Hedgehog comic book series and spin-offs. In this media, it was a base of the Egg Carrier and Dr. Eggman's operations when he tried to use Chaos, which only existed in the altered timeline created by the Super Genesis Wave.

Trivia

 * Near the end of the level, there is a particularly slow-moving platform which leads to four extra lives. This was most likely intended as preparation for the battle with the Egg Viper within the level itself. In the final game, the battle was split from the level (so progress is saved), so the extra lives are unnecessary. However, they were possibly left there for the player﻿ to discover.
 * Beyond the capsule, there is an unused tunnel that is blocked off, but it can be accessed using the Light Speed Dash. It was intended to trigger the cutscene for the Egg Viper battle within the level itself. However, in the final game, the battle was split from the level. As a result, a capsule was implemented and the area was sealed off, probably due to the difficulty of the level.
 * An unfinished duck Badnik was intended for this level, but completely removed in the final game. It can be found in pre-release copies, where it shoots at the player and attempts to run away.
 * A Sonic doll appears in Gamma's story, and he is required to shoot it as commanded by Dr. Eggman. The Sonic doll also appears in Sonic X, where the E-Series use the doll to train within the Egg Carrier.
 * In the tubes in the room where the Final Egg is reached, Metal Sonic and Silver Sonic II can be seen. One of the missions in Sonic Adventure DX: Director's Cut requires the player to bring the burger statue to Metal Sonic.
 * At the end of Amy's level, where there is a choice of paths, if one were to choose the wrong direction, the monitor changes between an Eggman symbol and what looks like a Poké Ball from the Pokémon series.
 * In Amy's version of the stage, there is a small section that Sonic does not explore at all in the first act.