On Magic Armor: Why would a Force spell grant resistance to magic? I would expect such an effect from a Metamagic spell. Perhaps it should be more like a physical barrier, so an in-game effect like 1 or two points of defensive strength could be interesting. Perhaps with a 100% chance to wear of per turn. So a mage can use it to protect himself from an attack but sacrifices the ability to cast something else for it. So its basically an "retreat or hope the enemy moves away" promotion.
Alright, the resistance to magic could seem a bit odd depending on the role of Force energy within the setting (which I must confess, I'm a little unsure of... anyone? A little help?). That being the case, make the
Mage Armor promotion be exactly like the
Magic Resistance promotion EXCEPT for the actual resistance to magic. Basically, a small resistance bonus against each energy type.
I've considered several different takes on mage buffs and since you almost always want your casters to cower at the bottom of your stack, never defending unless no other option exists, any bonus to their defense stat is going to be a mixed blessing. With that, I'm disinclined to advocate a defensive bonus. What if we had the promotion give the mage a withdraw chance (30 - 50%, whatever seems good) so when they get jumped by an Assassin they'll have a chance of surviving thanks to their protective magic. This wouldn't work in town but I find most of my assassination attempts occur in the field... I bet that sentence is going to set off a few flags for some Homeland Security 'net sniffing protocol. The promotion should vanish after the unit withdraws (if possible) or after combat (if not).
As I'm writing this I have another idea for the force or dimensional spheres: Stasis Field - the caster gets immobile and immune to all damage until he dispels it, but he can't do anything as long as it is active. This spell can be balanced by effecting only the caster or the whole stack, or by being affected by Dispel Magic.
I've also been debating about impassible barrier spells (
Wall of Force,
Bigby's Interposing Hand and
Force Cage anyone?) and I think they're a bad idea. The AI would probably have a hard time knowing how to use them effectively and a player would have a very easy time thwarting the AI with them. Just find any sort of natural choke point... and close it. I think all barriers need to be destroyable through combat OR you forgo barriers entirely and disable the enemies movement (which is functionally equivalent but the AI can handle that). If I had to think of an effect for
Stasis Field I would make it give the unit a very large withdraw chance but deny them all XP gain (effectively turning them into Loki). So they can't really die but they also can't learn (like that warrior of Mulcarn's that is trapped on the island in the Ice scenario...). In fact, the more I think on it the more that sounds like a spell for the
Ice sphere...