The spell Red Sign of Shudde M'ell allows an investigator to ignore one of a monster's special abilities other than Magical Immunity, such as Magical Resistance.
I would like to know how the timing of the spell in conjunction with equipment usage affects the value of a combat check.
For instance, an investigator faces a monster of type "Witch" with the special ability Magical Resistance, armed with an Enchanted Knife (+4 combat check, magical weapon) and a Red Sign of Shudde M'ell. First, the investigator equips the Enchanted Knife, using up one hand, and then equips the Red Sign with the other hand.
How much skill check bonus does the investigator get? There are two possibilities:
1) The Enchanted Knife is used against the Witch first, but only gives +2 combat check because of the resistance, so the investigator rolls the two additional dice. Then the resistance is removed by the Red Sign, giving a total of only 2 bonus. Since the order in which the items are equipped is important, the player should've tried to cast Red Sign first (because it can fail).
2) Even though the Red Sign was equipped after the Enchanted Knife, the player must retroactively apply the removal of Magical Resistance against all Magical Weapons equipped in case the Red Sign was successfully cast. After rolling the two dice for the Enchanted Knife against the magically resistant witch, the investigator can remove those two dice from the pool of rolled dice and then roll an additional four dice to take its place (since the Enchanted Knife would give +4 combat check given the absence of Magical Resistance).
The first case is easier to calculate using a spreadsheet program because more cell values become immutable. The second one is harder because it involves adding a means to reset the current calculation and a more complicated conditional expression to evaluate all skill check value bonuses depending on the presence and subsequent negation of monster special abilities.
The tactical decisions are more pronounced when there are more hand resources to allocate, such as Marie's third hand for spells. The player using Marie can decide how to allocate the third hand based on the resulting successes of the rolls resulting from the equipment and Red Sign used for the first two hands.
To recap: How is the Red Sign of Shudde M'ell supposed to affect the value (i.e. number of dice rolled) for a combat check based on the timing of its use? Does it matter whether you use it first or last? Why or why not?