The forces of the Unseen Evil marched into the field. The general smiled as it saw the adventurer’s mistake. “Destroy them! Show no quarter!” His army flooded the field, slaughtering adventurers left and right. A few casters near the back of the adventure’s party ran off into the night, possibly abandoning their friends, possibly for reinforcements, but it would be too late anyways. The day was theirs. The general laughed at the victory. None of his forces were injured, for nobody had thought to bring a silver weapon to the fight.
Werewolves, Axe-Mace Trolls, and Vampires have something in common. They are all monsters which are well known for having weapon immunities. A weapon immunity (in the event you are not familiar with the terminology) is when a creature is immune to a weapon call or type. The most common type of immunity is being immune to everything except a particular weapon call (e.g. magic.) Weapon immunities have been overused, and should be avoided whenever feasible.
Usually, weapon immunities are given to monsters as a way to balance how many PCs can affect a monster at any given time. If a creature is only effected by magic, then only people with magic weapons can kill the creature. This can bring a 4 PC to 1 NPC ratio, close to 1 PC to 1 NPC ratio. So, what is the problem with this solution? The problem is now only 1 out of every 4 PCs are able to help directly in the fight. It is creating cool moments for PCs with magic weapons, but for everybody else there is nothing to do other than be killed. This is amplified with newer players who often do not have magic items, plot items or anything besides the sword they walked in with. So, what can be done instead? Weapon vulnerabilities.
Weapon vulnerabilities are a different way to handle similar situations. Rather than having NPCs that are only affected by magic, the NPC is affected by every weapon. However, should the weapon be magic, the NPC will be harmed more. Good examples would be to have magic be armor piercing or have the NPC dying to a hit from magic regardless of where the blow landed. This allows all players to participate in the combat. It allows people to defend themselves should they be attacked, but it also gives cool moments to the people who have magic weapons. Are the NPCs still being surrounded? Perhaps they should have a power to keep people away or fight in a location where nothing can get behind it. Restricting PC movement, such as on stepping stones, can help overcome PC numbers without having NPCs that only a few people can kill.
In recent times Lightning Bolt has become a popular spell, and when many PCs have it, it can become frustrating to the NPCs. On the flip side, if the enemies are immune to lightning bolts, the PCs will be frustrated, because they are being held back simply because the NPCs can’t block. Here is a suggested solution: give the NPCs one use of resist magic which activates against the first magical blow the NPC receives. A fighter with a magic sword or a well placed magic missile can remove the immunity the NPC has, leading to a follow up attack from the lightning bolts. Instead of just being immune to lightning, now the players can make tactical decisions, discover how the defenses work and act in a dynamic manner.
Please note that I am not saying it is never appropriate to call “No effect”, for sometimes it is. If the creature can be killed by hitting it in a particular order, then it’s fine. If it can only be affected in honorable combat or after a ritual is completed, that is fine. If you have to lure a creature to where a boulder will fall on it, that is fine. All of these can lead to epic moments for the PCs involved and those who solve it. Compare those to the following. A new player has spent the last hour sneaking through the woods avoiding monsters. He sees someone fighting a creature with a magic weapon, hurting the creature, but losing the fight. The newer player sneaks behind the monster, and stabs it repeatedly, just to have the creature call no effect because the new player didn’t have a magic weapon. This turned an epic moment into something lame.
Of course, sometimes the story will dictate that only the mythical sword of the past can slay the major villain. Or perhaps, you just want it to be that only one PC can fight the bad guy at a time. Here are some suggestions to allow more than one person to effect the final villain, while keeping things more fair. The weapon that affects the bad guy has a drawback and harms the user more and more each time it is used by the same person to draw blood (first hit takes the limb holding it, second kills the wielder, third scalps, fourth and subsequent are voluntary ticks for example). The ancient sword is not any particular sword, but is rather a sword blessed by a being, and the blessing lasts for one swing. The being can give the swings out how it wants, perhaps requiring actions to be done to earn them. The boss must be defeated honorably, and each person only gets one try. The boss swings boulder but isn’t immune to any weapon style. Instead the magical sword give protection from boulder (or something else similarly strong), allowing other people to fight if they wish, but at a higher risk. These are all methods for a boss to be only affected by one person at a time, but still not require it to be only one person who gets to try and have fun killing the boss.
So, as an event holder, how have you avoided giving your NPCs invulnerability to different weapons? Have you ever had a moment where NPCs calling no-effect were just frustrating? Tell us about it in the comments!