I hadn't known about Circular Wall of Shields. Thanks!
The Treacherous Spear uses the wielder of the affected weapon's skills to attack, probably for ease of play. Would a sword controlled by a maga's spell use her Single Weapon Ability, her Finesse, or something else?
Edit to add: Or, if the base of 5 skill with average characteristics given by ezzelino above is more appropriate, how much would an additional magnitude improve that by (if at all)?