Courtesy of a script written up by Kyle, please enjoy the anonymous statistics on the race changes caused by the Metamorphosis Plague here:
http://www.swcombine.com/~kyle/Stats/RaceChange.php

This page updates automagically as new race changes occur, so it can be refreshed until the free race change deadline on Year 14 Day 55 at 17:00 CGT.

Count refers to the total number of changes recorded, Total Races Stats displays the net changes across each race, New Races Stats provides a breakdown of changes to each race, and Old Races Stats provides a breakdown of the changes away from each race.