pepper combo:
down attack -> forward air -> down attack -> forward air
do this over and over again. It will carry them to the edge of the stage and end up spiking them.
Viewing post in Super Tilt Bro. for NES comments
Nice you found it, it was actually the first Pepper's combo voluntarily designed in her moveset.
It is really strong, but the careful opponent has a number of options: first if they bait your down attack they can punish it as it is quite slow. Second, if not perfectly executed, it is not true and the opponent can react before the forward-air (also you need a fastfall between forward-air and down-attack). Finally, the opponent can tech instead of crashing (pressing down+direction before hitting the ground), making it a tech-chase situation.
It is possible the AI implements none of those strategies, but if you play against an human it should not be gamebreakingly good, but still a powerful move to be feared ;)