Hello!
Indeed it is a
billon denier formerly attributed to Nicholas Redwitz (Klaus von Redwitz) as
ban of
Severin (SW
Romania, near Danube). More recent studies assigned these issues to the Wallachian ruler Dan II. During the past years they've become less
scarce than in the past, as relatively large numbers were found in
Serbia, Croatia, W
Bulgaria. Usually they're awfully struck, yours is relatively nice for the
type. I've also seen specimens
overstruck on copper,
billon or even silver flans of other coins, sometimes cut to reduce
weight.
Good luck!
Bogdan Costin.