Egg Heart is the final boss of Sonic the Hedgehog 4: Episode II. The boss fight takes place in the second and last Act of Death Egg mk.II Zone. Dr. Eggman pilots his Egg Mobile into a human heart-shaped machine surrounded by several large electrified rings.
The Egg Heart, as its name suggests, is a mechanical contraption resembling a human heart. It is surrounded by four ring-shaped barriers that occasionally generate electricity. One half of the Egg Heart's body is blue while the other half is red.
The battle takes place on the Egg Heart's gravity rings, with each ring serving as a continuous circular ground platform, with the player spawning on the outermost ring. The player must reach the innermost ring to where the Egg Heart is located at. One way is to use the Copter Combo to fly there and the other way is to have Sonic run around until the rings intersect, then jump to the next ring, and do this once more to get to the center ring. When the player gets to the Egg Heart, they can damage it by attacking the cockpit Eggman is sitting in.
After the first hit, various sections of each ring will become electrified; either constantly or for a brief period. There can also be patterns dictating which ring sections are briefly electrified which switch between intervals. Touching the electricfied sections will damage the player. When multiple adjacent ring sections are constantly electrified, the player can will have to use the Copter Combo to safely reach the Egg Heart. After three hits, some sections of the rings will break apart. After taking more hits, a force-field will surround Eggman, which the player must destroy by using a Rolling Combo. In this phase, Eggman will also charge up a gravity-based attack that gradually darkens the Death Egg, create a black hole effect, and slam the player against a wall if they take too long to hit the Egg Heart. The player should repeat until the Egg Heart is destroyed. It takes eight (console) or five (mobile) hits to defeat it.
- This is the only boss ever in the Sonic franchise that is based on an organic body part.
- It is the only boss that cannot be defeated with just Super Sonic.
- The Egg Heart has similarities to the Psyco-Egg, which is the final boss of Sonic the Hedgehog CD. Both final bosses have objects surrounding them (Electrified ring for the Egg Heart, and four rectangle blades for the Final Fever) and both have some way to shield themselves: a force field that cannot be broken unless the player uses the rolling combo for the Egg Heart, and the four rectangle blades for the Final Fever (although they are there from the start). Both bosses are also located in huge mechanical bases, which are the final Zones for both games.
- Just like a real heart, the Egg Heart beats during the battle.
- By alternating hits on the Egg Heart as regular Sonic and Super Sonic, the player can skip the in-level cutscenes where Eggman revolves the Egg Heart's rings aroundm, allowing the boss to be defeated more quickly.
- The theme of the Egg Heart contains a portion of Splash Hill Zone Act 2's music from Sonic the Hedgehog 4: Episode I.