The Amoeba Droid boss fight has been described as "an evolution of the type of boss the original Sonic 2Zone had".
The Amoeba Droid is a metallic gray sphere with yellow and black hazard stripes on the upper half, a red Eggman Empire logo with a red "X" underneath it on the front, and a blue bottom. It also has three prominent prongs on it, each one with internal yellow and blue components.
The Amoeba Droid is able to levitate in midair and can control Mega Mack telekinetically, allowing it to mold this volatile substance into a number of things, like a liquid cocoon around itself for defense or projectiles to be thrown at opponents.
While able to control Mega Mack, the Amoeba Droid cannot generate this substance itself. As such, it relies on external sources to draw Mega Mack from. This, in turn, exposes the Droid's weak spot for an opponent to attack.
In Sonic Mania, the Amoeba Droid is fought with Sonic, Tails or Knuckles. In Sonic Mania Plus, it is fought with Sonic, Tails, Knuckles, Mighty or Ray.
The boss fights begins when the Amoeba Droid fall into the arena from the sky. As its first move, the Amoeba Droid will drop down into the blue Mega Mack below the arena and collect it, creating an impenetrable barrier that not only protects it, but will also damage the playable characters if they touch it. It will then bounce along the ground three times while chasing the characters. Afterwards, it will hover in the air and mold its gathered Mega Mack into small orbs of chemicals orbiting it around the middle that cause damage upon touch; while the Amoeba Droid can now be safely attacked, the orbs' orbital inclination steadily changes, meaning there is a chance the player can still get hit when attacking this boss. Afterward, it will eventually release all its chemicals, which will damage the playable characters should they hit them. It will then sit still midair for a split second before diving down into the Mega Mack below again, where it gathers up the blue chemicals and repeat the cycle.
After six hits, the Amoeba Droid will be defeated. The player can then touch the Goal Plate that falls down from the sky and finish the Act.
If a Super State user deals the final blow to the Amoeba Droid while it is still coated with the Mega Mack, the player will revert to normal form and take damage immediately before the machine explodes. This has been fixed in Version 1.04/RC 1.05.0713 update where the player no longer takes damage in that scenario.
↑While not listed in any instruction manuals, the internal files in the PC release of Sonic Mania refers to this boss as "AmoebaDroid".