Can't fly; he's not technically on foot. I give the divine plaque of protection, ethereal, maybe the magic resistance item, or crown of command and hold up a huge block that can't hurt him. Lore of beasts is good for that combo.
Slann cannot be put on a flying carpet for the same reason he cannot cast the Lore of Beasts #6 spell... its lame but "thems the breaks!"
I like both types of Slann. And just to be a stickler, higher state of consciousness does not make you eathereal, it makes him incorporeal. Which basically means the slann isn't immune to terrain effects as are ethereal creatures. As for equipment, I like the divine plaque, and an amulet of magic resistance to protect him. Mostly run shadow, so can use the fly spell in the lore for moving him around. Then load up with characters, use the slann to charge something and switch places with one of the combat characters. Another interesting tactic is to move him up into a forest where the opponent can charge him. As he is stubborn while in the woods, he can hold them there for a unit to flank charge the next turn.