Curseling , Vessel of Chaos ability help?

[modnar]

Greetings,

I was looking over the warscroll of the Curseling and got into a little discussion with friends about his Vessel of Chaos ability. The warscroll states: 

If this model successfully unbinds a spell that is possible for it to cast, it can immediately attempt to cast that spell even though it is the enemy hero phase. If that spell is successfully cast, it cannot be unbound.

"possible for it to cast"  What limitations are we talking about here? Can he only cast like arcane bolt & mystic shield? Or can he cast anything apart from specific faction spells which are written down as  " Only  Faction  Wizards can attempt to cast this spell."?

Thanks ahead!

[MitGas]

9 hours ago, modnar said:

Greetings,

I was looking over the warscroll of the Curseling and got into a little discussion with friends about his Vessel of Chaos ability. The warscroll states: 

If this model successfully unbinds a spell that is possible for it to cast, it can immediately attempt to cast that spell even though it is the enemy hero phase. If that spell is successfully cast, it cannot be unbound.

"possible for it to cast"  What limitations are we talking about here? Can he only cast like arcane bolt & mystic shield? Or can he cast anything apart from specific faction spells which are written down as  " Only  Faction  Wizards can attempt to cast this spell."?

Thanks ahead!

I'm pretty sure it's about spells that target army-specific things - units and the like. Generic things like dealing damage or buffs that are generic enough (e.g. not alluding to a particular unit or mechanic from another faction) to work for another allegiance are fine for him to cast in return.