Monster made from Lego pieces by Mike (5)
I believe the answer is:
golem
'monster' is the definition.
(type of magical creature in Jewish folklore)
'lego pieces by mike' is the wordplay.
'pieces' indicates anagramming the letters.
'by' is a charade indicator (letters next to each other).
'mike' becomes 'm' (phonetic alphabet: alpha, bravo, charlie etc.).
'lego' with letters rearranged gives 'gole'.
'gole'+'m'='GOLEM'
'made from' acts as a link.
(Other definitions for golem that I've seen before include "creature of Jewish legend?" , "Animated figure" , "Artificial human of Jewish legend" , "Human image brought to life" , "Animated artificial human from Jewish folklore" .)