No Errata
Q: What happens when I use Shadeglass Sword with the ploy Mighty Swing, targeting more than one enemy fighter?
A: You make the Attack action against each fighter in turn, in the order you choose. After the first of these Attack actions to be successful, you discard the upgrade, which means you cannot resolve the Attack action against any remaining targets.
Q: What happens when I use Daemonic Weapon with the ploy Mighty Swing, targeting more than one enemy fighter?
A: The fighter suffers 1 damage before making each Attack action, so they would suffer 1 damage, then (assuming they survive) make their first Attack action, then suffer 1 more damage and then (assuming they survive) make their second Attack action and so on. If they are taken out of action, you cannot resolve the Attack action against any remaining targets.

Skytear