Is it a suffix, prefix, stem change, clitic, what have you. Does the language really make a big deal out of plural/singular(/dual?/paucal?!) distinctions? If there are none, or there are things that could only be rarely used to be plurals, that's worth mentioning also!
I have an idea I want to test, but I need lots of data. IPA transcriptions would also be really awesome, but don't fret if you can't provide it! Thanks!