Mortis's page

Does a synthesist change size if he synthesizes with an eidolon of a larger size? E.G if a halfing synthesist synthesises with a medium eidolon does he become a medium creature?

I've noticed that no statistic is mentioned for the Save DCs for its Forest Magic ability. Given that this is a series of spell-like abilities should we use CHA? It could be argued, that given its nature that maybe is should be WIS based.