This isn't a new form of Wisdom. What you have sumbled across, is the Anti-Form, a form that Sora changes into when you use your Valor, Wisdom, or Master forms frequently.

There are many serious drawbacks to having Anti-Form, such as not being able to use items, use magic, or pick up refresher orbs. You can't Revert back, and it gets rid of all allies currently in the party. You also take 20% extra damage for the exchange of 50% increased speed, both attack and movement.

How it works, is that you get one point (on an invisible counter), for everytime you turn into one of the lower three forms. If you go Anti-Form, your points drop by 4. Everytime you go Final, it drops by 10. If you have recently obtained a new form, the counter will go back to 0, including activation of the Final Form.
0-4 points = 0% going Anti
5-9 points = 10%
10+ points = 25%

Once you get Final Form, (after Memory Skyscraper), the points will reduce back down to zero, and evetytime you go Final, your points drop by ten.

Also, the chance will change, depending on the circumstances.
Normal scripted battle: x2 percent
Battle against Organization XIII: x4
Battle with a non-cooperative character (I.E, Hercules, but not Auron): x0
Battles against Xemnas: x10

There are some battles that going Anti will be beneficial, but most of the time, it is not. You also do not get EXP from defeated enemies, if you defeat them while Anti'ed.