@Andrew: I usually try to keep the amount of explanation I add to my code in a relation to the amount and helpfulness of the information provided by the person asking the question (think of who's providing the MWE here, and who should be). But since you're asking... :-)
So this code mainly relies on biblatex's
\bibfont, which is the probably the safest (and most elegant) way to customize a bibliography's style. I'm appending
\footnotesize (that's 10pt in a 12pt environment) to whatever else is already contained in
\bibfont. I'm also switching to a right rag, which is a nice thing in bibliographies, and a must when working with columns that narrow. Then there's
multicols, restricted to the bibliography only. One might also try using
\onecolumn instead of the multicol package.