When does a pursuer in a chase make a check to notice my sudden illusory hiding place?

Question

According to Can I use Minor Illusion to create a wall, hide behind it, and attack with advantage?, if I am being chased, round a corner and create an illusory 5×5 crate via Minor Illusion (and they do not see me cast it) I can successfully hide behind it to elude my pursuer.

What's not clear is whether and when my pursuer would be able to make an Investigation (Intelligence) check to penetrate my illusion. What would trigger their Intelligence (Investigation) check against the crate? What if they just kept running? Does a pursuer investigate everything they come across during a chase?

Answer 1

This is highly situational.

The spell only says that someone seeing the illusion can make a check. This prescribes nothing about when would someone do that. But it does say that it is an action, so the observer has to decide to do it. They also have to investigate the illusionary object itself. Strictly by the wording of the spell scanning an area for illusions is not allowed. (To me it would seem reasonable to allow it with disadvantage on the check, but that depends on the GM.)

The main deciding factor here is whether the pursuer can suspect there is an illusion there. The type of the area (back alley or royal ballroom) and the observer's familiarity with it will be important, but the final decision is up to the GM. (Creating the illusion of footfalls still running away might help you too.)

Do not forget that you still have to hide, which normally takes an action and involves you rolling a stealth check. The illusion merely allows you to do it in a place you couldn't otherwise.

This also means that the pursuer might be able to simply search for you (using perception). He could do that if you were hiding in/behind a real crate, your hiding place being illusionary does not hinder this at all. This way he does not even have to roll investigation.

Answer 2

To determine whether or not the pursuer would perform an investigation check, the pursued first needs to pass a perception check. This check would be passive perception because it is a chase and the pursuer would be noticing things like a lack of foot prints or leading somewhere else or some other clues that indicate you have stopped running and may be attempting to hide. If the pursuer passes the perception check, then he would investigate for your location.

The passive perception would be when the pursuer comes around the corner at the earliest. If not then, It would be whenever the pursuer completely loses track of you if they kept running past your hiding spot.

Example 1: you successfully created your illusion after coming around a corner into an open market place and the pursuer loses sight of you. The pursuer then comes around the corner, sees no possible trace of you. His passive perception should be competing against an easy check because you shouldn't have just disappeared. He passes, and begins to investigate where you could have gone.

Example 2: you cast your illusion in a side path around a building where you have more paths to go by and more corners to go around. The pursuer fails the passive perception and just runs around another corner. After a while, the pursuer completely loses you and decides to start back tracking and investigates your possible location

Answer 3

Probably never!

Investigating a Minor Illusion uses an action, and the pursuers in a chase "are strongly motivated to use the Dash action every round." (DMG 252) Unless there's a compelling reason not to Dash, the pursuer shouldn't have a chance to do any investigating.

Whether there's a compelling reason is dependent on the situation and how the DM envisions the setting of the chase. If your pursuer is just 10 feet behind you and rounds a corner to find an alley with 30-foot walls that's completely empty except for one 5-foot crate, that pursuer is realistically motivated to take a look at that chest.

(But the DMG assumes that chases take place either in generic cities or in generic wilderness, and in cities where there's always a 5% chance you'll run into a beggar and a 5% chance you'll run into a pack of dogs, it can be assumed by the laws of cinema that whatever alley you turn down is full of crates, or barrels, or piles of junk that you can blend into.)

Assuming your hiding place makes sense, under "Ending a Chase" (DMG 253) it says a chase "ends when one side or the other stops, when the quarry escapes, or when the pursuers are close enough to their quarry to catch it." When you hide inside your illusory crate, you stop. So the chase ends.

However, the next sentence is weird: "If neither side gives up the chase, the quarry makes a Dexterity (Stealth) check at the end of each round [...] The result is compared to the passive Wisdom (Perception) scores of the users." The phrasing is awkward, but you haven't "given up the chase" because you haven't fallen down exhausted or turned around to surrender.

The DMG lists various reasons for you to have advantage or disadvantage on your stealth check, and I think we'd all agree that being completely obscured by an illusory crate qualifies. (Depending on the situation, there may be a strong motivation for the DM to say you succeed automatically.) With passive Perception scores being what they are, and advantage being what it is, it's very likely that you'll succeed on this check, in which case "that quarry [who is you] escapes." The pursuers have failed, and would only bother taking a look at any individual crates if the DM were feeling especially sadistic.

If you fail your Stealth check, "the chase continues for another round." You're still not moving, though, so the chase immediately ends again—That doesn't make any sense. This is where the chase rules break down for our purposes, because you have effectively withdrawn from the paradigm of a chase. Your failed Stealth check has betrayed your general location, and now the pursuers are just plain old NPCs. They will or won't investigate your illusion based on the normal rules of Investigation checks, because the chase is has ended.

Answer 4

Situation and GM Dependent

Unfortunately, there isn't a clear-cut answer here. There are several factors that a GM should take into account when determining what to do in this case (and in most illusion cases in general.) For this case, the considerations include:

1. Are there other creatures around?
2. Did they say you run into their midst and 'create' a crate that you then disappeared into?
3. Are you or your pursuers known by them (and on friendly or unfriendly terms?)
4. Would the crate be out of place in the location you created it?
5. Are the pursuers familiar with you, your magic, or magic in general?

The key here is that the illusion itself isn't what would 'tip off' the pursuers. It would be that the illusion is out of place or that other passers by may tip off the pursuer that something is amiss.

The best use of illusion is to create something that someone expects to be there. You aren't trying to draw attention to the illusion, you are trying to draw attention away from the illusion. If the attention is drawn to the illusion, then that would be when an investigation check occurs. That attention may be an out of place crate, it may be others pointing out what just happened, it could be any number of things.

And don't forget to Hide

The Hide action is your friend here as well. A crate that has the sounds of heavy breathing or shuffling as you maintain your position will be a giveaway. Don't make it easier than it already may be for them to notice something is wrong and want to Investigate.

An example

In one of my own games, we were pursuing someone through city streets. When we rounded the corner, our quarry wasn't to be seen, but the DM described that people were acting a little surprised and we rolled a perception to see if anyone seemed out of place. A clue was given that one person was being observed more than others and I cast Dispel Magic on that person thinking that they were under some sort of Disguise Self or similar magic...and the quarry was revealed.

Answer 5

Forget the illusion

You are hiding behind a crate, illusionary or otherwise, your Dexterity (Stealth) check is compared to their passive Wisdom (Perception) if they are just passing by or an active check if they spend their action to Search.