Every form but final +1 anti-point
Anti-form -4 points
Final form -10 antipoints
Gain a new form points are reset to 0
Transform while a part member is passed out +0 anti points

During scripted battles x2 multiplier on points gained
During battles with extra allies x0 multiplier on points gained
During a disney villain fight x0 multiplier on points gained
During an organization fight x5 multiplier on points gained
Armored Xemnas fight x10 multiplier on points gained

0-4 anti points means 0% chance of anti-form
5-9 points gives you a 10% chance
10+ points gives you a 25% chance

0% chance of going into anti-form when transforming outside of battle

Basically if find yourself getting into anti-form too much you probably have wracked up a lot of anti-points. So go stand by a save point and enter final form a few times to drain your anti-points that way even if you have to use multiple forms or spam limit form your chances for anti-form will be low.