Hyper Knuckles

From Sonic Retro

Hyper Knuckles is a super transformation similar to Super Knuckles in that it makes Knuckles the Echidna faster, invincible, requires fifty rings and makes him glow. It also saps away rings at the same rate of one per second.

However, in addition to requiring the seven Chaos Emeralds it requires the seven Super Emeralds from Sonic 3 & Knuckles, which are obtained by entering a Giant Ring with the Chaos Emeralds. You are then warped to Hidden Palace Zone, where you are required to complete one of the Special Stages, which are the same Special Stages that you would get the regular Chaos Emeralds from in Sonic & Knuckles alone.

Hyper Knuckles looks exactly like Super Knuckles, but with the addition of after images. If he should touch a wall while gliding, it creates a wave that destroys all on screen badniks.

This character was only available in Sonic 3 & Knuckles and has not been in any game since.

In the American Sonic the Hedgehog comic, where characters' "Super" forms have different names, Hyper Knuckles is the name of Knuckles's Super State.

Sonic the Hedgehog series characters
Heroes	Sonic (Super, Hyper, "Dark Super", Darkspine, the Werehog) | Tails (Super, Turbo) | Knuckles (Super, Hyper) | Amy Rose | Cream | Blaze (Burning) | G.U.N. | Silver (Super)
Anti-heroes/Neutrals	Shadow (Super) | Rouge | Chaotix | Mighty | E-102 Gamma | Chaos | E-123 Omega | Emerl | Rogues
Villains	Dr. Eggman/Dr. Ivo Robotnik | Metal Sonic | E-Series | Biolizard | Black Arms (Black Doom) | Gemerl | Fang
Other	Gerald & Maria Robotnik | Big | Chao | Tikal | E-101 Beta | Flicky | All Characters