Scandinavian monster right in charge (5)
I believe the answer is:
troll
'scandinavian monster' is the definition.
(monster in Scandinavian mythology)
'right in charge' is the wordplay.
'right' becomes 'r' (common abbreviation).
'in' means one lot of letters goes inside another.
'charge' becomes 'toll' (toll is a kind of charge).
'r' put within 'toll' is 'TROLL'.
(Other definitions for troll that I've seen before include "Ugly dwarf or giant" , "Folklore monster" , "Fish - gnome - sing" , "cyber-bully" , "supposedly lives in a cave" .)