I'm playing a custom class in a Pathfinder campaign that gets an ability similar to the Magus' Imbue Weapon and has access to the spell Greater Magic Weapon. One of the big things this class has going for it is the ability to expend spell slots to grant the weapon bonuses.
I have just learned that Pathfinder has a rule that a weapon cannot have an effective bonus above +10 for any reason. (This was different in 3.5, which is the reason I didn't know.)
The current GM was unaware of this rule and OKed the class at the time. After discovering this rule, it makes one of the main class features practically worthless, for that reason the GM is allowing it to continue for the time being.
Is the ability to create a weapon that temporarily exceeds the +10 cap going to be broken?
Here are some details:
The Imbue Weapon ability on this class allows the character to expend a spell slot to grant an equivalent bonus to his weapon. He does not have an arcane pool.
The class is capped at 6th level spells. (Bard Progression)
This means, at level 20, he could have a +1 weapon with +9 in special abilities, cast GMW on it to make it a +5 weapon with +9 special abilities, and use Imbue Weapon to add +6 worth of special abilities to the weapon for a grand total of +5 weapon with +15 in abilities.
Imbue weapon lasts for 1 minute.
He can only Imbue his own weapon, which is treated like an Wizard's Arcane Bond. It only works for him.
Most (nearly all) of his class features require him to expend spell slots to use, so he runs out of spells very quickly.