As Mario, getting up from ledge is normally dangerous against Ridley. Of course, if he chooses to not to ledge trap, your OK. However if he does, Mario might be in trouble. First, we have to understand Mario's options at ledge. Mario can wait at ledge, neutral getup, roll getup, jump getup, or getup attack. Ridleys nair actually covers every option except wait at ledge if timed correctly. Ridleys down-smash covers all options except jump getup, so stay on your toes. Despite there only being 5 real options, dropping from ledge is also an option, though it is risky, requiring to use your jump immediately, but it gives you time to throw out an aerial right by ledge, to swat Ridley away. However, Ridley could take advantage of this by then using fireballs to push Mario away, so now he's offstage without a jump. Statistically, the best option is jump getup. But don't always use the option, as if you do Ridley could read it with an up-smash.
Mario