The problems I see with the plan:
1) Without Energon Cubes we severely limit our own capabilities to affect the battlefield. Our plan is still to fell the leader of the smaller group quickly, and the spells to do so are likely to exhaust us.
This might be addressed if we give Lyssa 4 cubes and keep 2 per character. She already has 7 on her while we and Thais only have 4.
2) How does the 'ignition crew' escape? Note that the dwarven volunteers are very slow. The enemy might be unwilling to follow them into the minefield, but this isn't going to deter the mages. An archmage is not going to be stopped by a mine - they can do some truly ridiculous feats. Once the Watcher's Creature and the archmage (a Shade? what else could it be?) catch up to our rearguard, our people are likely to be doomed. We should give them some means of quick escape.
This might be addressed by getting rid of half of the gold and making the carriage available again. Or we might spare a chariot or two to pick them up. Or something.
Edit: If that is of any consolation, the gold might distract the enemy and slow them down if their discipline is not all that great (if they are alive, they have a use for the gold). If they are forced to ignore it by the mages, this might affect their morale, too.
3) Not to be 'that guy', but wasn't it mentioned that the spells that require maintainance can not be placed on the ring?
3) Spells that require maintenance would not work. Or rather they would and then they would instantly end.
I know that 'GM giveth and GM taketh away', but still.
This needs to be clarified. Lyssa does not know 'Mass Fear', so maybe she can 'cast' it from the ring, and then maintain it, even though she does not know the theory behind it?
We probably are better off if we stick to illusions. The crows aren't
that intelligent.
If you address those (especially the 2nd), I can consider the plan. It is tempting, but I'd rather not leave our crew behind if something goes wrong.