1988 nickel 0

[Tridmn]

Double plancet, is that even possible?. Can see ridge with naked eye. Last pic from from from wrong nickel.

[Woods020]

I am newish, so more experienced collectors may have a better explanation. However it looks like a rim fin that has folded over. This is something I learned from a post here as well asking about a similar issue with a Mercury dime. Maybe research rim fins and see if that looks like the coin you have.