Hard Boiled Heavies

The Hard Boiled Heavies (ハードボイルドヘビーズ), abbreviated as the "HBH", are a group that appears in Sonic Mania. They are a team of elite Egg-Robos created by Dr. Eggman. After being struck with the power of the Phantom Ruby however, the Hard Boiled Heavies began displaying power that even Eggman could not have predicted.

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
The Hard Boiled Heavies were originally a group of five elite Egg-Robos tasked with handling the hardest missions that their creator, Dr. Eggman, would have them perform. Upon reading a promising new energy source on Angel Island, the Hard Boiled Heavies were sent to investigate and retrieve this energy source, the Phantom Ruby. Upon excavating the mysterious gemstone, the five Egg-Robos got transformed into more powerful forms when the gemstone caused time-space to warp around them. As a side effect to this newfound power however, the robots went insane.

The Phantom Ruby transported the Hard Boiled Heavies, along with Sonic the Hedgehog, Miles "Tails" Prower, and Knuckles the Echidna, to the Green Hill Zone. After making their escape, the Hard Boiled Heavies planned to keep the Phantom Ruby for themselves. However, they soon met up with Eggman, who took the Phantom Ruby from them, leaving the Hard Boiled Heavies to take their their leave.

As the three heroes progressed onward, they would each encounter and defeat the different members of the Hard Boiled Heavies in specific areas: the Heavy Gunner in Studiopolis Zone; the Heavy Shinobi in Press Garden Zone; the Heavy Magician in Mirage Saloon Zone; and the Heavy Rider (Sonic and Tails only) and Heavy King (Knuckles only) in Lava Reef Zone. The Heavy King in particular made an attempt to steal the Master Emerald, but was stopped by Knuckles.

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 Klepto Mobile 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.

Trivia

 * The Hard Boiled Heavies are a similar group to the Robot Masters from the Mega Man series, as both groups are composed of robots created by an evil scientist and each of them are fought throughout the game, and are re-fought in the last area.
 * The Heavy Gunner is the only member of the Hard Boiled Heavies that serves as an Act 1 boss. All other members appear as Act 2 bosses.
 * The Heavy King is the only member of the Hard Boiled Heavies who does not use "Hi-Spec Robo Go!" as his boss theme like the others, instead sharing Eggman's second boss theme with the Weather Globe in Studiopolis Zone and Gachapandora in Metallic Madness Zone.