In Sonic Mania, the Death Egg Robot is fought with Sonic, Tails or Knuckles. In Sonic Mania Plus, it is fought with Sonic, Tails, Knuckles, Mighty or Ray.
The boss fight begins when a lock-on target starts flashing and the Death Egg Robot slams down. Over the course of the battle, the Death Egg Robot constantly moves to the right, chasing down the playable character. Along the way, it will destroy any vertical wall it hits. If the player takes too long to beat this boss, they will arrive at a cliff that ends with a bottomless pit.
The player's objective is to attack the Death Egg Robot's body. Over the course of the battle, it will utilize two types of attacks. The first attack has the Death Egg Robot lock onto the playable character when they are close enough before launching out its claw for about three seconds. Making contact with the robot's claw will damage the player. While its claw is launched out however, the player can use its outstretched arm as a platform to reach the robot's main body for a clear hit. The Death Egg Robot's second attack has it launch bombs at the playable character when they are far enough, which will explode shortly after hitting the ground.
When not using the Death Egg Robot's arms to attack it, the player can use the hill and platforms that appear along the path to gain enough jumping height to safely reach the Death Egg Robot's body with a Spin Jump (before the Death Egg Robot destroys them).
Upon taking six hits worth of damage, the Death Egg Robot starts to walk faster. If the player manages to hit the Death Egg Robot twice more, it will break down and hit the ground, causing any raised platforms on-screen to be destroyed, before falling off-screen through a hole in the ground. The player can then proceed to the Capsule and finish the Zone.
The original idea for the Death Egg Robot to be fought in Green Hill Zone was by Takashi Iizuka.
This is the first time that the Death Egg Robot is not fought in a space station.
When destroying the floor below it upon defeat, the Death Egg Robot destroys as well any foreground plants above said floor. As a result, it often leaves random pieces of these flora being left outside the area where the mech fell, giving the screen a slightly glitched look.
It should be noted that the Death Egg Robot's legs inflict no damage to the playable characters if they touch them, allowing the player to get behind the Death Egg Robot and easily hit it.