Every now and then you will see a Neclos with a little plastic crystal/gem in its chest. Usually blue green or red.
Even rarer still are the ones like this.
I thought it was plastic until I actually got one into my greasy claws. It seems to be pewter or aluminum (maybe steel). Definitely metal of some sort.
Reminds me of some sort of Ganondorf Totem
I always just assumed it was plastic, but after reading this I checked my Darqueen and you're right!
The Neclos figures with removable pieces seem to be some of the least common in the line. The Darqueen figure in particular is a tough one to get, especially with the chest piece included.