Phantom Heavies

The Phantom Heavies are modified versions of the Hard-Boiled Heavies that appear in Sonic Mania. They are a team of elite Egg-Robos created by Dr. Eggman. After being defeated by Sonic and his friends, They were heavily modified for their next encounter with the trio in Titanic Monarch Zone.

Concept and creation
Christian Whitehead came up with the Hard-Boiled Heavies after imagining Eggman entering a state of depression after Sonic the Hedgehog 3 & Knuckles; instead of going after Sonic, he would merely lounge at home in his pajamas and that the abandoned Egg Robos would go "a little mad." After thinking about this concept, the term came into being.

History
When Sonic and co. got to the Titanic Monarch Zone, four of the Hard-Boiled Heavies, now modified into Phantom Heavies, returned during the heroes' climatic fight with the Phantom Egg. Upon reaching the Egg Reverie Zone, the Heavy King, now modified into the Phantom King, tried to steal the Phantom Ruby and use it for himself, prompting Eggman to battle the Heavy King using his Kleptomobile in an attempt to take the gemstone back. Sonic, having all seven of the Chaos Emeralds, transformed into Super Sonic and defeated both of the power-hungry monarchs however. With the Heavy King's defeat, the Hard-Boiled Heavies seemingly ceased to exist, but ultimately their fate remains unknown.