Thanks for the weight.
That seems to be 16% under weight.
(2.5g-2.1g= .4 .4/2.5=.16=16%)
I believe normal tolerance is 10% or .25 grams above or below normal weight (of 2.5 grams for a zinc cent).
All I'm saying is that it has the appearance of a grease filled die, but it also appears to be an under weight planchet also.
How about adding an image of the reverse?