If I had a wax golem who gained sentience and has a level in synthesist, would he be immune to Banishment as it allows Spell Resistance, and said golem has the beloved Spell Immunity (ex)?
...a wax golem who can summon an eidolon? Well, the eidolon could be banished, as it doesn't have Spell Immunity... I'd have to double-check how synthesist works, but I thought that, if targeted by a spell, then between the eidolon and the summoner, if one of them isn't immune, then the spell goes through. Since the eidolon doesn't have spell immunity, the eidolon could be banished. That's my thought on it.
But seriously, a wax golem that can summon and bond with an eidolon? I love this game.
Actually, I believe if the summoner is targeted by a spell, then the worse of its two types is used (construct or outsider) to see if the effect works. Banishment works on outsiders, so it can target the synthesist, but the synthesist has spell immunity, so I figured it would kick in :P