Hola,
Regarding the legends, I had say the Catholic Monarchs (Ferdinand II and Isabella I) :
Observe "[FERNAN]DVS [ET ELISABET]"
Reverse "[REX ET RE]GINA C[AST LEGION]
First I thought it was a 2 maravedis as well because of its weight but it's most likely a 4 maravedis because of the octofoil and its size.
I see a "C" left to the castle ; that seems to match with the Cuenca mint. The ensayador is not visible on your coin.
http://www.monnaiesdantan.com/vso6/espagne-rois-catholiques-maravedis-p1337.htm
4 Maravedis de los Reyes Católicos,
Ceca : Cuenca (C latina a la izquierda)