your int. score is halfed for all things except spellcasting, for that the penalty is doubled!
tell me what you think of this item,please!
A flaw is not an item, its a flaw 
That said, there is already a Flaw called "simple-minded" which amounts to the same thing, though without reference to spellcasting. The way the existing flaw is written I suppose it could be applicable to a magus, but doubtful anyone would want to play a simple-minded magus lol.
For magi, I might suggest absent-minded, ala the absent-minded professor. I suppose there must be more than few doddering Bonisagi library/lab-rats who fit that description.
Hey, if my Int score were negative, I wouldn't mind it being halved.
Int is never used for any casting! It is Stamina you use. That is, unless you use a house rule..
Good catch
It is used for sponts. But in stressfuyl situations it tends not to be used, yup. Besides, the point of making it non-applicable precisely to spellcasting sounds like pure powergaming to me. I would triple the malus for spellcasting, at least.
Xavi
I changed the flaw sumwhat.
Only if HR so (which we did consider when transfering to 5th) - the RAW uses Stamina.
Really? We hadn't noticed that change.
Xavi
Yeah, I know. Somethings you keep missing even if you shifted through the book or even read it from cover to cover multiple times.
You're awesome, Fruny.
It could be an item. Some warped mage with too much time on his hands could have made it as a prank. Probably a garment or piece of jewelery enchanted with a Perdo Mentem effect and hmmmm... a Creo Vim effect?
Yes, what YOU describe IS an item, something that someone could make. What abe has proffered and that which is the title subject of this thread is a FLAW (an innate character defect), NOT an item.
Any story ideas that could come from this flaw?
Yes. Lots. What are your ideas?
Can't think of any off of the top of my head,that's why I asked you.
Oh come on abe, you have a good imagination, give us a story idea in which your spell might be used, you can do it!
ok then how about this a problem ucures that only an idiot can solve!
what sort of problem could you imagine that an idiot might notice that others (who think of themselves as more intelligent and astute) might not pay any attention to?
Maybe he/she is blissfully playing with a pet mouse and it runs into a hole in the covenant foundation but doesn't come back out and when the idiot peers in to try and see the mouse, he/she feels a gust of wind and the smell of strange flowers issuing from the hole.
When he/she tries to tell the magi about it they ignore him. Until later when a strange serpent comes out of the hole and threatens the covenant! 
that's the sort of story idea I meant!