[Nikolai]

Originally Posted by Clipper

You must have a Mojo in play to play Double Mojo, or else it would be discarded.

Originally Posted by MunchkinMan

However, Clipper is correct about the discarding issue.

Really? I'd say your quote from the rule book is pretty clear in that you are simply not allowed to play a Double Mojo card without a Mojo in play.
You can't play it anyway to discard it afterwards, for instance because you want to avoid Charity.

So I'd say it is clear that even if wanting to play very strict and not wanting to give the player a "not-so-experienced-bonus" (although I would absolutely recommend a less strict play style in general), the player should have taken back the Double Mojo to his hand, he should neither have been required nor allowed to discard it.

Unless this part in the rules means one is allowed to discard a Double Mojo card *from one's hand*:

Originally Posted by Munchkin Zombies rule

s, p. 4, top of right column]
You can discard a Mojo card at any time, even in combat: "I don't wanna be a Plague Zombie anymore."

Does it mean that?

But even then I'd say he shouldn't have been *required* to discard it as a consequence of mistakenly trying to play it, because playing doesn't equal discarding from his hand.