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

Hold L + R then press B(2), Y 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 R dunk modifier, run toward the basket and press the one foot 180 gather (Y). As soon as the gather motion starts, quickly rotate the Analog-stick counter-clockwise twice then press the Windmill Dunk (Y) again. Release Y 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 R modifier must be held for the entire dunk. Also, you must complete the 720 motion before pressing Y the second time to dunk.