Well itachi didnt use his mystery twice

If a mystery is interrupted the first time, it doesn't really count as being used in that turn, other than it going on cooldown and consuming chakra.

Itachi's mystery doesn't incorporate a cool down even if it is interrupted since it can be used 2x before its cool down starts. If you interrupt a mystery it doesn't count as "activating a mystery skill". so that ninja can still use its mystery if it didn't have a CD on it.

This works with anybody. Say Sage Naruto queues his mystery and you CC him before he gets it off. If wind main pops dance, he can cast it again and it will go off that round.

Agree with most people mentioned here. Also, I'd like to add that this also works with Normal Gaara. When the user decides to use Gaara's barrier in round 2, and that you have some ninja that give enough chakra for him to cast mystery, a wind main c*e impetus to remove the activation cooldown and Gaara would be able to cast his mystery the same round its barrier has been set up.

as others said, interrupted mysteries aren't actually considered as used. Imho mysteries that cost 0 or 20 chakra should be accounted as used, but this is not how the things work now.

thanks I see