[Sai'ix Renkai]

Spiritomb, i'll put it here for you.

Kiba negates the effect of a mission. Simple, yes?
Unfortunately for you, it's not a mission effect letting it be put in play. If Kiba said "Negate that mission" or "Negate target mission" it would work. But it says to negate it's effect. Which it doesn't even have until it's put in play, which makes it too late for Kiba to negate.