Looks like a a piece of a clad dime tore off and attached itself to the copper plated cent. How? That would be interesting to figure out. But I don't think it is a mint error.
We've discussed this before. When advertisements are sent with coins glued to them the impressions are backwards and can peel off and stick to another coin. I'll have to search for the thread.
First of all, welcome to CT. Interesting find. Have you tried to see if it will lift off? Maybe soak it in acetone for an hour or two and then use a wooden toothpick to see if it will lift off. If it is glue, it should come off, if not, ???.
You are working pretty hard to save a penny. I think it is more interesting the way it is. Sure, find out what happened, but, otherwise leave it as is.
Good for you to at least think to research it! I'd 2x2 it just because 2x2s are cheap! Keep searching!!!!!
Either way,even if you dont get rich off of it. It's still pretty cool. Especially to find in your pocket