1968 S Nickel, Polished Die And Maybe Something With MM.

Filled die or chip on the lower portion of the MM?

Grease Fill on the TIC and die chip on the MM. Great photos so we can see clearly.

The mint mark issue maybe a damaged punch issue. When the punch bends a bit it alters this area often. Probably these best way to tell if it is a damaged punch issue is to compare with listed RPMs. If this is the case, then you will see several of the dies showing it for that year/s around. Depending on how many years they used the punch. (some years it only last a short time because of many dies made those years. other times when few dies were made those years, then it lasted longer. the same punch was often used on different denominations as well)