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 craft into a human heart-shaped machine surrounded by several large electrified rings.
The player must jump from ring to ring to reach the Egg Heart. When the player gets to the Egg Heart, they can damage it by attacking the cockpit where Eggman is located at. After the first hit, lasers will start electrocuting some of the rings. The player can use Tails to fly to 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 use the Rolling Combo to break apart. Eggman will also charge up a gravity-based attack that will make the Death Egg dark, create a sort of black hole effect, and slam the player against a wall if they take too long between hits. The player should repeat until the Egg Heart is destroyed. It takes eight (console) or five (mobile) hits to defeat it.
- 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.
- There are actually two different ways to get to the center ring where the Egg Heart is. One way is to use Tails to fly to the center ring, and the other way is to have Sonic run around until the rings intersect, then jump to the next level, and do this until he gets to the center ring, but it can only be done before the rings begin to break apart.
- 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 theme of the Egg Heart uses a portion of Splash Hill Zone Act 2's music from Sonic the Hedgehog 4: Episode I.