While playing Theme arena i found something interesting about Ibiki's mystery.

You need firemain or someone who transfer first debuff.

Before Ibiki use his mystery, he automatically gets Immobile on himself (before he hit enemy ninja with mystery) and when you have Firemain mirror, this Immobile which Ibiki gets will go back on Enemy (causing edo itachi to transfer it back to you) then Ibiki use his mystery and fully debuff enemy ninja.

As you can see on this videobefore Ibiki cast mystery, he transfer his own debuff to enemy team because if your Firemain mirror.

https://www.youtube.com/watch?v=bFObFCJk9zM