My father taught me, many years ago, that a wizard’s most important skill is not spellcasting, but fraud – followed hotly by ingenuity.
In the vein of the “Banquet” spell of Better Than Any Man, I present “Baker’s Magic Fixing Spell”, which he came up with long ago. There are two versions, plus the ostensible effect, which you may feel free to insert into spellbooks, etc. This is presented as Open Game Content (see the sidebar for the license).

Pistori’s Most Expedient Repairing Dweomer
(AKA Baker’s Magic Fixing Spell)

Level: 1
Duration: See Below
Save: Conditional. See Below.
Range: Touch.
Components: Verbal, Somatic, Special material (see below)

Blurb when found inside spellbooks:
This first-level spell appears to instantly and magically repair any one mundane tool or other useful item, including weapons and armor.
The material component is a small jar of foul-smelling, acrid ungents (including the anchoring fibers of a mussel and pure alcohol distilled from wood) and the broken object itself.

Effects:
Version 1: The Original
(This is the one my dad first wrote up; simple, to the point, and slightly worse than Mending. But a LOT funnier.)
The spell instantly and completely repairs one broken and useless non-magical item/tool/whatever. It cannot be cast upon a whole and usable item or on magical items. It can regenerate missing parts if they are irrecoverable, and to all tests the item is perfectly sound. It functions perfectly while performing routine tasks, as well as the first time it is used under stress.
The second time the item is used in any situation of danger or stress, it catastrophically and utterly irrecoverably fails, preferably in an incredibly humiliating manner – armor rots to rust and horrific stains, swords turn soft as rubber, lockpicks shatter and jam in the lock, etc.

Version 2: The Weird one
(This is what the spell evolved into over about 20 years of play. I still occasionally inflict it on my players, and it can get really fucking amusing even if they know what’s going on. It leads to resource games – “how much is having that set of lockpicks REALLY worth to you, hmmm?” – and encourages gambling)
The spell instantly and magically repairs one broken and useless non-magical item/tool/whatever. It can regenerate missing parts if they are irrecoverable, and to all tests the item is perfectly sound. It functions perfectly while performing routine tasks.
Each time it is used in a life-threatening or stressful situation, however, the character must save vs. Spells (or make a Fort/Crushing Blow save for the item at a -1 for each time it is used). Failure indicates that some randomly-selected item or piece of property OWNED by the character (not necessarily carried on them) is irrecoverably lost or destroyed. This can take several rounds to take effect, and the DM is encouraged to make it look coincidental. For the purposes of this spell (and yes, this has come up in a game), slaves aren’t property but the title to them qualifies.
Casting the spell on a whole, currently usable item allows a save vs. Spells to avoid its effects entirely.
Broken Magic items are also allowed a save. If the item saves with exactly the number required, the magics of the item pervert the spell and fully repair it – but it is drained of all its significant powers for at least an hour. If the item passes the save with any other number, the Fixing Spell fails. If the item fails its save, it’s partially repaired, but fails catastrophically the next time it is used – violently and unpredictably releasing the magic within.
Whole and usable magic items will fight the spell, draining the item of some power or charges, but inflicting at least 1d6 of damage on the caster per significant ability it possesses.

Viewing the item in a proper reflective surface (blessed silver or polished iron, pure water) will show malicious-looking imps covering it, slowly devouring its substance. This spell is a Curse, should you desire to remove it, and clearly detects as such if you know how to look..