The Golden Egg was added to Core Keeper as a part of the game's very first limited-time event: the Easter Egg Hunt. When crafted, players will have the ability to display it prominently in their base, and take it into battle with them, and get some unique boss drops from using the Golden Egg.
How to Get the Golden Egg in Core Keeper
The Golden Egg is actually an item you will need to craft in Core Keeper. Doing so will require the eggs from the Easter Egg hunt. There are four different types of eggs: brown, rose, grey, and green. Each type of egg corresponds to a different Core Keeper biome, and getting them will require getting it from a drop after killing a mob from the biome the egg corresponds with. The Golden Egg will require five of each different types of eggs to craft. Players have discovered that creating mob farms, or farming the bosses and enemies they summon with them have been effective strategies to get the Easter eggs.
Once you have all 20 eggs you need to craft the Golden Egg, if you take it to the Wilderness biome and use it to summon the boss Azeos the Sky Titan, you will be able to fight a special variant of the boss. Awakened Azeos has the same statistics as the normal version of the boss, but will gift you with some special seasonal items as a reward for completing the Easter event in Core Keeper.