Shattered Kingdoms

Looking more for an answer from the Admin, but can mastered spells fail. This is assume of course the caster is not deafened, suffering armor penalties, etc.

I had contemplated not answer this, simply because I am not the final authority on this subject. But, since this is a question I'm sure more than one person may be curious about, the answer, I believe, is "Yes". Many years ago, Dulrik changed the wording from "perfect" to "mastered" to reflect this modification. Do remember, failing a spell and having saving a spell are two different things - even though their messages can be identical.

In all my years of playing, however, I have rarely seen this happen.

Yes, it can happen. Though it is rare. I've seen it happen with spells I have mastered as well as innate spells, but I have yet to see a mastered skill fail (such as languages, unless the other party isn't mastered in it).

I've seen mastered pick lock fail.

lol

Hate to come off like a jerk, but is there an authority that can say with 100% accuracy?

This would also come off like a jerk but I know the response. Test it many, many times and you tell us.

I know when it comes to brewing, regardless if your mastered at brew and the spell itself you can still fail

I can say with 100% authority that mastered means you can still fail, though rarely.

This is indeed why Dulrik changed it from perfect to mastered.

I've never seen a mastered spell fail if the caster was not deaf and was without armor penalties. Skills, yes. Spells, no.