Superman's greatest weakness is often considered to be green Kryptonite, the amber shade of Kryptonite is much more dangerous. Green Kryptonite de-powers him and causes him pain, but different colors have different effects on Kal-El, some even being a little sillier than serious. Some, however, have dire consequences and can even cause harm to others around Superman.

Originating from his home planet, Krypton, green Kryptonite weakens Kal-El similarly to radiation poisoning for humans. Many of his vilest enemies use the substance against him to bring Superman down to their level, Lex Luthor being among the most famous to use Kryptonite. Because of this, it's considered his Achilles' heel and the most powerful Kryptonite color, but the amber Kryptonite that spawned from his worst nightmare is even more powerful.

Superman's Worst Fear Come Alive

Amber Kryptonite was first introduced in Dark Nights: Death Metal - The Last 52: War of the Multiverses #1 by Regine Sawyer, Alitha Martinez, Mark Morales, and Emilio Lopez. It is vastly more powerful than green Kryptonite and spawned from the Dark Multiverse, which was formed from the worst nightmares of DC's heroes and created twisted versions of themselves or loved ones. Originally, the amber Kryptonite is used by a dark version of Lois Lane to kill Superman himself after he accidentally kills her son Jon. Using it absorbs all of his powers and gives them to her. She then manages to use his abilities to decapitate him in a brutal way as revenge for her son. She even disperses the shards of the Kryptonite to her people rebelling against superheroes.

Superman losing his life is no doubt terrifying, but the worst part of this kind of Kryptonite is not the death, but the dispersal of his powers. Any villain who uses it against him will steal Superman's powers and ultimately can use them for their own personal goals. The knowledge that his powers could be used to harm others is the scariest thing Superman can imagine, making amber Kryptonite his true biggest weakness, The repercussions of amber Kryptonite being used is shown very clearly in Dark Knight: Death Metal - The Last 52: War of the Multiverses #1 in the story No More Superheroes. The Dark Multiverse Lois proves this by stealing Superman's powers to advance a cause of violence against powered people. She strikes down Superman himself, and it's shown that she even kills Wonder Woman and Maxima. She doesn't hold back and kills without thought, spreading the idea of violence and pain throughout the world. Clark and Lois' nightmare versions of themselves spread havoc without mercy and nearly end the world just because of amber Kryptonite.

Kal-El's fears manifest themselves through the harm of others and very rarely does he fear for his life over that of another. Amber Kryptonite steals the powers he uses to protect people and gives those who wish harm to the world the power to do so. Green Kryptonite may de-power him, but it's amber Kryptonite that is Superman's true biggest weakness.