I was cruising through some old material and was reminded of the wild magic of ADnD 2e. Then I was reminded that I had done a 3.X conversion. I admit that the flavor of the old wild magic is a little verbose, and requires a goofy table for level fluctuation, but I really liked and enjoyed that much variance. While this has been done plenty of times over the years, here is my simple take on a more Pathfinder friendly version by implementing it as an arcane school as well as including a taste of wild magic to other casters via the feat.
Wild Magic School
Wild mages revel in the wild magic that is inherent in the magic they manipulate.
Level Fluctuation (Su): You gain Wild Mage as a bonus feat, except that you do not need to make a concentration check when using wild magic. In addition, every spell you cast varies in the actual caster level used to determine the results of the spell. When determining caster level, roll a d20 and consult the level fluctuation table to get your effective caster level. Additionally, if your die roll is equal to your level, the check results in a wild surge.
Elemental Roulette (Sp): As a standard action you can throw raw magic, targeting any foe within 30 feet as a ranged touch attack. Roll 1d6 to determine what type of damage the raw magic does: 1-acid, 2-cold, 3-elec, 4-fire, 5-sonic, 6-force. The damage is equal to 1d4 + 1 for every two wizard levels you possess. You can use this ability a number of times per day equal to 3 + your Intelligence modifier.
Chaos Manipulator (Su): At 8th level, you gain the ability to affect the outcome of items that normally have a random result.
When using magic items or casting spells that result in a random result, you can roll twice and choose the result you want. At 12th level you roll three times, at 16th you roll four times, and at 20th you roll five times. You may only ever select one result.
This effect extends to items that you draw from: such as bag of tricks and deck of many things.
By harnessing the chaos inherent in magic, your spells become more powerful, yet unpredictable.
Prereq: Ability to cast arcane spells, any metamagic feat.
Benefit: When casting a spell, you may attempt to add a metamagic feat that you have without increasing the effective level or casting time of the spell. Choose a metamagic feat that can have an opposite effect, such as enlarge spell or extend spell, and roll 1d6 to determine the effects of the metamagic feat on the spell. On a 1, the opposite effect takes place. On a 2, the spell is affected by merciful spell. On 3 or 4, the spell is cast as normal. On 5 or 6, the metamagic feat is successfully added to the spell.
The strain of infusing wild magic into your spell requires a concentration check to successfully cast the spell. If the metamagic feat adds +1 to your spell level, the DC is that of vigorous motion (10 + adjusted spell level), while a +2 feat has a DC of violent motion (15 + adjusted spell level) and a +3 feat has a DC of extremely violent motion (20 + adjusted spell level).