Super Friends: Rest in Peace - S3.E30

The Super Friends mourn the death of Batman (a.k.a. Bruce Wayne) and have gone into hiding after the Legion of Doom unearth a crystal called "Noxium", created by one-time member Dr. Natas. The crystal emulates the weaknesses of each member of the JLA such as kryptonite, Yellow Power and lethal energy. It can then kill all of the Super Friends. The Legion of Doom then plans to take over the world after they have disposed of the Super Friends and the crystal, only for it to be found and disposed of in deep space, allowing the Justice League to stop the Legion, who finds out too late they were in hiding and had really killed off their android clones.