I saw a tricky Magic Resistance question for ArM today, and I find it a frustrating demonstration of the MR rules, and a potentially exploitable rule.
RacconMask wrote – How does this react with Target:Part? If I take (for example) a javelin or spear, and cast a Target: part spell to control the butt of the spear’s haft to attack flawlessly with Rego… does that get magic resistance when the un-controlled tip stabs in? Thinking here of an ‘invisible swordsman’ ReFo spell that only controls the hilt of a weapon.
Grumble. It is a great idea as it demonstrates again how MR in ArM can be complicated. Truthfully it is no different from enchancing a soldier with a spell to increase their toughness, and insisting that they use normal weapons. Which is to say the players at the table need to understand a simple rule – When a rule is exploitable it can be used by everyone, and the GM has far more resources. Do you really want your enemies to react in the same way?
As long as the exploit is applies consistently and it feels congruent in the story, let the players exploit. Then hit them with it.
This is the same for Parma Magica burning spells. They look great on paper, and are exceptionally dangerous, but they also will likley impact the players far more once the NPCs adapt.