Tartarians come to mind, so long as you can heal the likely Feeblemind...
Any commander you've Enslaved.
Monsters with exceptionally high movement (there are some that can fly 10 provinces a turn, ex. Vastness... which also reveals another interesting property when GoR'ed) are likely picks.
If you're fighting R'lyeh illithid packs, you might also want to GoR a mindless unit to make a mindless commander for leading additional mindless troops.