I've been developing a character named Sinistar for quite a while now that's meant to defeat my brother's Incantatrix/Initiate of the Sevenfold Veil monstrosity, and I've decided that there are only two sure things.
1) Death.
1) Taxes.
2) Immunities.
He's a Warforged Juggernaut, and I've been trying to make him immune to all forms of energy damage. His race (and that class) make him immune to a host of things including nonlethal damage, positive energy, poison, mind-effecting effects, and others. I've been trying to find ways to make him immune to every other element of damage, give him a way to block spells, and make him only fail saves on a one (and be able to reroll those.). Mystic Shield is an awesome spell to have as a constant effect on a character like this. It'll severely limit the number of spells that can be directly used against you, as it protects against all effects of 6th level spells and under.
Yes. All of them. You could even dodge the book-to-the-face-via-DM caused by using that to be immune to the wall of stone the wizard drops on you.