Tiny shape-shifter
I believe the answer is:
amoeba
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">tiny shape-shifter</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for amoeba that I've seen before include "Protozoan life form" , "Tiny organism consisting of single changing cell" , "Basic life form" , "Tiny one-celled animal in water" , "shape-shifter" .)