Illusion Magic and its Effects on Cover
Illusion magic might be one of the biggest banes when it comes to players and the GM. Everyone has ideas on what the Illusion effects should be, but no one ever agrees when the spells are cast. Part of this problem stems from poor communication between players and the GM, and just having a conversation can help fix misconceptions and miscommunications.
But before that conversation, you must decide on how Illusion magic will work in your game. For the purposes of clarity, we are going to work with the 5E rule sets based on the Player’s Handbook. For a brief description of Illusion magic check out page 203 in the PHB under the section The Schools of Magic.
Imagine during a tough fight, there are bandits peppering a wizard full of bolts and arrows. On the wizard’s turn they figure out a way to make it harder to hit him and he uses his action to cast Minor Illusion and create what looks like a 5 foot by 5 foot stone wall in front of him that he can duck behind to give him cover from the attacks by the bandits. Now what? How do you go forward to determine what the bandits do?
For me, this is all going to start at the basic level of a campaign. How prominent is magic in your world? Would, for the sake of the argument, a low-level bandit with average intelligence know what is happening? Obviously they would know something is up, there wasn’t that stone wall there just a moment before, but they have no idea if it is real or not. How do they determine if its real?
Well, per the rules of Minor Illusion they can either spend their action on an Investigation check, or they can determine it isn’t real with physical interaction. A bandit with 10 Intelligence isn’t going to waste their time puzzling this out, but rather use what they have on hand, their crossbow. If the wizard is standing behind the illusionary stone wall, the bandit will try and shoot the wizard’s exposed body. So the bandit lines up his shot on the exposed squishy parts of the wizard, pulls the trigger and launches a bolt at 300 feet per second at his target.
Mechanically, how will that work? Does the wizard have cover? Does the wizard get to enjoy any bonuses to their AC? If you crack open your PHB and jump to page 196 and look under the Cover section, the obvious answer that jumps out to you is… maybe? The book makes mention of actual objects providing that cover, but no mention of how to mesh these rules with illusionary cover, so we will just have to make our own.
Cover provides two bonuses, one to the target’s AC and the other to the target’s Dexterity Saving Throws. The purpose for the bonus to the AC is that there is less of them exposed, which makes it harder to hit them, whereas the bonus to the Dexterity Saving Throws comes from part of the blast being blocked by physical objects in the way.
One way to take this would be that the wizard will get a bonus to their AC, how much depends on what they conjure. If its a short stone wall, it would be +2, if it is a tower shield that covers most of them it would be +5. If the wizard then drops prone and hides behind their illusion, they would have total cover and be unable to be targeted by the bandit. The illusion would provide no bonuses to their Dexterity Saving Throws as it does nothing to block a blast of magical energies.
A second way would be instead of a bonus to the wizard’s AC is that the bandit has disadvantage on attack rolls against the wizard. The wizard doesn’t have true cover as the cover can’t stop a bolt from hitting the protected parts of the wizard, but the bandit doesn’t know that just yet. As before, this illusion would provide no bonuses to Dexterity Saving Throws. This method does step on the toes of the Blur spell with no concentration requirements or spell slot expenditure, so keep that in mind when determining which method you want to go with.
Going with either of the options above, and the bandit hits, we are finished with the bandit’s turn and we continue. The real complications come if the Bandit misses on an attack against the wizard. How do we determine if his bolt went through the cover or went wide above the wizard’s head? It could be as easy as you deciding that the first unsuccessful attack the bolt shoots through the wall and the bandit knows the illusion is fake or as complicated as a d100 roll with a hundred different outcomes that somehow involves the bandit slipping on a banana peel. But let’s go a different route, one that hopefully feels a bit more authentic.
When the bandit shoots a bolt at the wizard, there are two options. A hit or a miss. A hit is easy to conclude, roll your damage and move on with the bandit unaware that the wall is an illusion. A miss is where it gets sticky, and we are going to draw on another illusion spell, Mirror Image. When you cast Mirror Image, you are protected by illusions of you and when you are getting attacked you roll to determine if it hits one of the other illusions or you. We will use that same mechanic for our purposes, but change a few things around.
On the bandit’s miss, we will roll a d20, on an 11 or higher the bolt flies through the illusion and the bandit has an inkling something is wrong. The next miss, roll a d20 and on an 8 or higher the suspicion of the bandit is growing as a second bolt passes through the wall. On the third miss, roll a d20 and on a 6 or higher, the bandit knows that the wall is fake as the bolt flies through it. This allows the wizard to feel rewarded for their smart planning, as well as provide authentic interactions between the party and their foes.
This system can also be adapted for different intelligence scores. If a creature is incredibly smart, they may only need a single d20 roll with a 6 or higher to realize that the cover is actually an illusion. If the creature has a really low intelligence score, they need more rolls on a d20, the first one needing a 15 or higher, second one 13 or higher, etc, etc. While we don’t have hard set rules on this, it’s easy enough to determine how quick an opponent might guess as to what is real and what is illusion using this system.
It’s easy to understand why Illusion magic is so difficult to work with and why players and GMs are slamming heads over this. As a GM, it’s easy to just ignore the wizard casting the illusion spells, but to create a living world, you will eventually have to interact with these illusions and its important to have a plan on how those interactions will work that both you and the player agree on. Nothing is worse than when you have these great ideas on mechanics and the players have completely different ideas, and you realize that this 30 minute argument could’ve been avoided had you just chatted with them beforehand.