Specifically I have a brown furred transmuter. I want to pick up a monstrification staff and use Powerful Change (Su) when I turn party members into gargoyles. Will that work? Or are you only considered the caster of the staff for setting the DC and caster level.
Yes, you're the caster. No, you can't use powerful change in this way.
Activation: Staves use the spell trigger activation method, so casting a spell from a staff is usually a standard action that doesn’t provoke attacks of opportunity. If the spell being cast has a longer casting time than 1 standard action, however, it takes the full casting time to cast the spell from a staff. To activate a staff, a character must hold it forth in at least one hand (or whatever passes for a hand, for nonhumanoid creatures).
It's your standard action being used, and you choose the parameters of the spell, so you're the one casting the spell.
However, powerful change only works on spells cast with arcanist spell slots:
At 3rd level, the brown-fur transmuter learns to harness the power of her magic to empower her transmutations. Whenever the brown-fur transmuter casts a transmutation spell using one of her arcanist spell slots, she can expend 1 point from her arcane reservoir as a free action to bolster the spell. If the spell grants a bonus to an ability score, the bonus then increases by 2. If it grants a bonus to more than one ability score, only one of the ability scores gains this bonus. The brown-fur transmuter cannot expend more than 1 point from her arcane reservoir in this way.
This ability replaces the arcanist exploit gained at 3rd level.
Spells cast from a staff use the staff's charges, not arcanist spell slots.
Isn't there a feat that lets you use your slot to cast a spell from a wand or staff? Then, since it is your slot, this might work.
/cevah