Something doesn't seem right to me. Will you post obverse and reverse images of the entire coin, please? Chris PS. You didn't need to post a poll. It is just an option.
I'd have to guess that it's a blob of solder. Look at the reversed impression on the blob and no weakness in the reverse strike. It cannot be a cud.
That was my first thought, too, but any weakness on the reverse would be at the top. That's why I wanted to see an image of the entire coin. Chris
After seeing the photo of the reverse, I'm 99.99999999% positive that this is PMD. Like @rickmp said, if it had been a cud, there would be extreme weakness, not only on the reverse, but on the obverse as well. There is just too much metal in that blob. Chris
The first pics make it look like the blob is raised, while the later pic makes it look like another coin might have been pushed into it. @Kadatabob is it raised or incuse?
It is pushed inward, like another coin left the reverse impression of the word Monticello into coin. My camera has issues. Or as you mentioned incused.
I believe that it is an error. It's an indent from another nickel. I have examples that I can show later this evening.
Here are some of my certified Nickels and Cents with indent. Most are Broadstruck but I have seen the indent on normal Nickels
Great looking coins Paddyman98, thanks for the examples. You also found what looks to be the same type of error, specially on the nickel. Appreciate the help.