The Egg Janken is an unused mini-boss found in the data for Sonic Mania's Studiopolis Zone. Similar to Gapsule from Sonic & Knuckles' Flying Battery Zone, it initially masquerades as a Capsule before transforming into a boss when the player presses the button on its underside.
Once activated, the Egg Janken will begin to cycle through different Rock-Paper-Scissors combinations on its two screens, the leftmost of which is marked "S" for Sonic, with the rightmost marked "E" for Eggman. The boss will hover from side-to-side across the arena while swinging its spikeball arms back and forth in an attempt to protect the button on its underside. If the player successfully presses the button, the combination currently displayed on-screen will be selected, with the boss reacting differently depending on the result:
- If the result is a draw, the boss will display a bored expression on its screens and simply try to strike the player with one of its spikeball arms, damaging them on contact.
- If Eggman's side wins, the player will hear a buzzer indicating a loss. The boss will display an angry expression on its screens and flip upside-down, then stretch its arms out to the sides, hover towards the player and finally crash to the ground, damaging the player if it makes contact.
- If Sonic's side wins, the player will hear a ping indicating a success. the boss will look distressed and shake violently while stretching its arms out to the sides, after which they come crashing back inwards, damaging the boss on contact.
Three successful hits will cause the Egg Janken to explode, ending the boss fight.
- Although this boss doesn't appear in the final game, it is fully functional and will work correctly if spawned within the level, though no Signpost will appear once the boss has been defeated.
- The Egg Janken has a much lower hit-count than any mini-boss used in the finished game. It's unknown whether this would have been increased had the boss actually been used, or whether this was a concession to the slower-paced nature of this boss fight.
- Although it is clearly a mini-boss, using the mini-boss music and involving neither Dr. Eggman nor the Hard-Boiled Heavies, the data for the Egg Janken is actually stored with Act 2 of Studiopolis Zone. It's possible that at the point in development when this boss was created, the transition to Act 2's level layout happened at some point prior to the boss fight, similar to Sonic the Hedgehog 3's Angel Island Zone where the Act 1 Mid-Boss, Fire Breath, is technically fought within Act 2's level layout.