Mischievous Irish elf (10)
I believe the answer is:
leprechaun
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mischievous irish elf</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for leprechaun that I've seen before include "Mischievous imp" , "Elf in Irish folklore" , "He helps Irish housewife" , "Mischievous Irish elf" , "Mischievous Irish sprite" .)