1984 US penny

[traps7]

I notice Doubling on Bowtie, ear and left shoulder lapel. The coin appears to have a pivot rotation with die clash. Doubling on Letetrs and date. The reverse also has doubling and die clash.What causes the slag on coin Thanx

[MintErrors]

This looks like a zinc cent that was struck too hard and it broke through the copper layer. That blue looking stain is from the zinc core. It's a form of damage. In my opinion, it does not hold any collectable value.

The green stuff may be verdigris. It happens a lot to copper coins, especially in high humidity areas and if some one is located near the ocean.