User blog comment:FairyRaven/Fairy Tail Chapter 356: Tartarus arc - Prologue, Review and Commentary/@comment-7418318-20131018145724

I don't think Cobra the Poison Dragon Slayer will be of much use against the Nine Demon Gates even if the former Oracion Seis join the battle on the good side.

"Poison? For a Demon that's a treat." Mirajane in Chapter 310.