Help With DIY Emerald Legion: the Immortal Do-Nothing

[Anthrowhale]

Making the build in the OP incorporeal should grant a 50% miss chance to corporeal fire spells, so that's something else to consider, I suppose. 50% miss chance, 50% damage -- although the damage on postmen will probably still be enough to overwhelm him. :/

The only ways I know to resist an Initiate of Mystra Mailman delivering Transdimensional Searing Orbs of Fire while projecting an AMF over you are:
(1) Via the static planar trait.
(2) Via a Multi-headed Lernaen Lumi.
(3) Via body-swapping.