OK, my new Druid character is helping the rest of the party defend against an almost limitless horde of undead, making a final majestic stand against the BBEG et cetera et cetera. So, being undead, I'm not going to bother with things that target fortitude, or poision effects, because they are pretty much immune.
However...
Control Winds has a "Fortitude Negates" save, which normally would mean that Undead are immune, EXCEPT, that undead are explicitly effected by any spell (with a Fortitude save) that would effect an Object, such as Disintegrate. Wind Effects specifically effect objects, namely, trees, buildings, and other structures.
So would a hurricane-force Control Wind in an Updraft setting just pile all the undead in its area into a neat column, just begging for a Flame Strike, with no save?
Combine that with an area-effect damage spell like Blistering Radiance, Vortex of Teeth, or even Blade Barrier, and its hard to see how this can't end badly for them, stuck as they will be in a giant slurry-maker....
Edit: I may have just found my answer, in that they do get a Fort Save, but the modifier is based on CHA instead of CON.