Giant Punch (ジャイアントパンチ Jaiantopanchi) is Donkey Kong's neutral special move. By pressing the special move button, DK will start swinging his arm around, charging a punch. Pressing the button once more will deliver the blow, which gains knockback and damage for every completed swing. If no button is pressed, after ten swings DK will become fully charged and stop winding up; his head will start smoking to indicate this. The fully charged punch can then be delivered at any time by pressing the special move button; the punch is weaker when used in midair.
If the player presses a shield button or presses the control stick left or right while charging, DK will save whatever charge he has and shield or roll. He can then continue charging later. Being hit while charging will cancel out any charge.
In Super Smash Bros. Brawl, DK gains launch resistance when he throws a fully charged punch, making it very hard to interrupt, and can be saved to defend against an incoming KO move. On the other hand, a punch that's just under full charge has significantly more KO'ing power.
 Reverse Giant Punch
When using Giant Punch in Brawl, if the control stick/D-Pad is quickly hit in the opposite direction during the first few frames, Donkey Kong will turn around very quickly (there is no animation, he simply faces the opposite direction) and will use Giant Punch in the new direction. Every character (with the exception of Sonic and Samus) can do the same with their neutral special as well.
Giant Punch has stages of being charged, these are recorded in swings of Donkey Kong's arm, each swing DK does increases damage and knockback for the punch, the charge has eleven stages in total, the eleventh stage is the fully charged stage. A fully charged Giant Punch will have a quicker animation resulting in a quicker punch and do the most damage but is weaker in knockback. In Melee and Brawl, all stages of the punch are weaker when used in mid-air.
 SSB stages
 SSBB stages
Here's a video showing off all the stages of Brawl's Giant Punch.
 Manual Descriptions
"Charge with B, then press again to punch. Quit charging with Z."