Not a mint error Had another coin stuck to it That crud may come off if you soak it in water. Or acetone if not water soluble You can’t really hurt it
Welcome to CT, looks like something stuck to it. Overnight soak in water, see if it comes off, then acetone. Could be solder too.
Looks like some melted Tootsie Roll on there…and the backwards N shows another coin was stuck to it. You could probably get most of that off with a wooden spatula, then soak in distilled water as advised previously, then acetone soak. The surfaces may be mottled looking afterward, no telling how that stuff is reacting to the metal. But if no reaction, then what’s covered might be brighter, after removal, than the rest of the coin. The rest of the coin will more than likely be toned and worn from circulation. Let us know how it comes out of the wash…imo…Spark
