Super Knuckles has a bright magenta colored pulse to his body and a magenta colored aura around him, but retains his basic physical form, unlike most other super transformations.
Powers and abilities
While in his Super State, Knuckles is granted the traditional invincibility towards any attack. All his physical attributes has as well be enhanced in this form: His strength has been increased greatly, allowing him to plow through any obstacles and his movements has been enhanced as well, vastly increasing his speed, jumping, gliding, climbing, etc. Like every other super transformation caused by the Chaos Emeralds, once he runs out of rings he loses his Super State.
Sonic the Hedgehog 3 & Knuckles
Knuckles is able to turn into Super Knuckles at the first time in Sonic & Knuckles as the player has collected all seven Chaos Emeralds from Special Stages. By then collecting 50 rings and pressing jump button twice, the player has activated the Super transformation for Knuckles. The player will lose one ring per second and when the ring count is on zero, Knuckles turns back to his regular form.
Super Knuckles appears in the final fight of the game to stop Metal Overlord from destroying the world, by using the emeralds thanks to Sonic's help he turns into his super form and not only gains a magenta colored glow, but a shield that helps him with his attacks too. In the end Team Super Sonic saves the day.
Sonic Chronicles: The Dark Brotherhood
Super Knuckles was also referenced in Sonic Chronicles: The Dark Brotherhood in the Chaos Emeralds part of the journal, stating that "Sonic, Shadow, Knuckles and a variety of people have been known to use the power of the seven Emeralds to transform into Super versions of themselves".
Sonic the Hedgehog (16-bit)
In the 2013 re-release of the original Sonic the Hedgehog, Knuckles is not only an unlockable game mode, but all seven Chaos Emeralds (and a new final Special Stage) can be enabled as a bonus with the enhanced level select code. By doing this, Knuckles can indeed transform into Super Knuckles with only the Chaos Emeralds, and is almost identical to his original appearance from Sonic the Hedgehog 3 & Knuckles. Despite this, Super Knuckles is considered completely non-canon in this game.
Knuckles' first known transformation into his super form was when he went head-to-head with Super Sonic in a battle for the Chaos Emeralds, their battle eventually destroying the Zone they resided in. Knuckles later turned into Hyper Knuckles again to battle Master Mogul, along with Super Sonic and Turbo Tails.
Knuckles later obtained his super form to fight Hunter on Angel Island using the power of the Master Emerald. In this form, Knuckles looks almost demonic and appears to be in pain when undergoing the transformation. As Super Knuckles, Knuckles was able to stop a spear which sends its victims to the Egg Grapes and proceeded to attack Hunter, picking him up, spinning him around, and throwing him into the ocean where he drowned.
Super Knuckles, unlike most other Super States, does not have a golden glow, but rather a magenta colored one.