When in the Slam Dunk Contest, tap Square, then hold Circle to do MJ's 1988 Slam Dunk. If you do it from the free throw line it is an automatic 50.

Hold L1 + R1 then press Square(2), Triangle to do the Vince Carter arm in the rim. If you hold it for a few seconds, he will put his arm pit in the rim for a 50 if you are lucky.

To do a 720 dunk for an automatic 50, while holding the R1 dunk modifier, run toward the basket and press the one foot 180 gather (Triangle). As soon as the gather motion starts, quickly rotate the Left Analog-stick counter-clockwise twice then press the Windmill Dunk (Triangle) again. Release Triangle just before completing the first rotation and you will automatically complete the second rotation. You will always get a 50 for completing this dunk. Note: The R1 modifier must be held for the entire dunk. Also, you must complete the 720 motion before pressing Triangle the second time to dunk.