A. With whatever weapon Zidane has equipped when using it. He has a Mage Masher equipped and uses Soul Blade, he can cast Silence on a target. Other ailments he can cast are:

Butterfly Sword=Silence
The Ogre=Darkness
Gladius=Slow
Exploda=Trouble
Rune Tooth= Poison
Angel Bless= Confuse
Sargatanas= Petrify
Masamune= Doom
The Tower= Mini
Ultima Weapon= Sleep

Q. How can Zidane's Thievery become a really powerful attack?