Mischief-maker to smile about the Spanish taking money (7)
I believe the answer is:
gremlin
'mischief-maker' is the definition.
(magical creature)
'to smile about the spanish taking money' is the wordplay.
'to smile' becomes 'grin' (grinning is a kind of smiling).
'about' is an insertion indicator.
'the spanish' becomes 'el' ('the' in Spanish).
'taking' is an insertion indicator.
'money' becomes 'm' (abbreviation in economics).
'el' enclosing 'm' is 'eml'.
'grin' placed around 'eml' is 'GREMLIN'.
(Other definitions for gremlin that I've seen before include "Imp causing mechanical problems?" , "Cause of technical fault" , "Fault-causing sprite" , "Troublemaking goblin" , "Cause of mechanical failure?" .)