The Juggernaut does have certain vulnerabilities. He can be affected by mystical forces of sufficient strength. Without his helmet and/or skullcap, both constructed of an unknown mystical metal, he is vulnerable to psionic attacks against his mind. Nimrod, a robot from the future of an alternate Earth, successfully attacked the Juggernaut's mind and nervous system with advanced weaponry producing tight-beam high-frequency sound waves and a synapse dislocate that jammed his neural impulses. However, had the Juggernaut used his force field, perhaps he might have proved invulnerable even to these futuristic weapons.
The Juggernaut once attempted to transform Black Tom Cassidy into a being like himself with the ruby of Cyttorek. The result was that both Marko and Cassidy were Juggernauts, but each had considerably less power than Marko had possessed when he was the sole Juggernaut. (Marko and Cassidy each claimed to have half Marko's previous power, but this is inaccurate, considering that the Juggernaut's previous power level was virtually immeasurable.) Marko finally regained his full power, and hurled the ruby into orbit so that no one else could ever use it.
Paraphernalia: The Juggernaut wears a helmet fashioned from an unknown mystical metal found in the dimension of Cyttorak. Wearing this helmet, the Juggernaut is able to resist all forms of psionic attack on his mind successfully. Recently, the Juggernaut constructed a skullcap from scraps of the metal he used to construct the helmet. He wears the skullcap under, his helmet. Hence, if his helmet is somehow removed in battle, the skullcap will provide him continued protection from psionic attacks on his mind.
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