'Nimbusartigem' is Dativ, the Nominativ would be 'nimbusartig', where '-artig' means like.
Artig by itself means something like 'well-behaved' used primarily for children and pets.
I don't think 'eingesetzter Pferdefuß' has anything to do with hats, apart from the regular meaning of 'Pferdefuß'
the only other I am aware of is 'a catch', like 'this sounds too
good, where's the catch?'.
This is because the devil has a horse's foot.
I don't think 'eingesetzter Pferdefuß' means anything exotic, but what you translated earlier, 'inserted horse's foot',
I assume it makes sense if you see the coin in question.
Yes, I see how 'inserted horse's leg' makes sense for this coin:
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Andreas