To perform a taunt, press P+K+J. This will increase the damage of your next attack as long as you don't get hit first. The damage bonus is cumulative, so the more taunts you perform in a row, the more damage your next move will do. It takes 2-5 consecutive taunts to kill an opponent with one hit, depending on the strength of the move used.
Pressing Down 3 or more times rapidly allows you to beg, which restores life for as long as you keep tapping
(don't tap
too much, you'll drain him).
You can only beg when you have less than 3 ballz of life remaining. Remember that you are vulnerable while you are begging.