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I'm a very fresh DM in 5e, having never played the game before, although I have played computer games based on DnD. Likewise, all of my friends are first time players so we're trying to teach each other the game as we progress. We decided to try play the Lost Mine of Phandelver adventure and it's going well, but I'm worried that as a DM I'm not really handling surprise properly.

For example, in the Lost Mines story it starts with the goblin ambush. In my case, once the party was quite close to the ambush, I rolled the stealth for each goblin and 3 out of 4 came under 15, which was the passive Perception of our ranger, so the ranger noticed the goblins while others were surprised (nobody was actively looking). I also took the approach that once either side notices the other and they aren't sneaking, combat starts (provided the creatures are hostile), so once the ranger noticed the goblins the combat was on and everybody rolled initiative.

However, is there a limit to passive perception, or does it extend to the edge of normal vision? So if a character is walking in broad daylight, can they spot a goblin ambush from, for example, 300 ft away, or is it up to me as a DM to determine if they have to be, say 50 ft from the ambush to notice? Likewise, would the goblins see the players advancing down the road from hundreds of feet away? I saw the section about the range of passive Perception to find traps in the player handbook, but nothing on this issue.

If I were to rely on my guts, I would say that the goblins can see the players coming down the road (no chance of hiding in plain sight), and would attack when the players are within 80 ft (normal range of their shortbow), while players would have no chance of spotting goblins hiding in the bushes, but this would mean the players would always be surprised, which I think would unfairly disadvantage people who have invested in Wisdom/Perception.

I know that I shouldn't get hung up on rules and ultimately it's my call, but I was just wondering if there is something written on this in the handbook that I have missed? I don't want to mishandle an important game mechanic.

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  • \$\begingroup\$ Related, although probably not a dupe: rpg.stackexchange.com/questions/48256/… \$\endgroup\$
    – user17995
    Jan 28, 2017 at 22:04
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    \$\begingroup\$ Just to clarify, there is no such thing as "passive Perception" itself. There are character's Perception and passive checks. "Passive Perception" is the same Perception, assuming you don't ask the player to roll a die, but use the passive number instead. \$\endgroup\$
    – enkryptor
    Jan 29, 2017 at 8:56

2 Answers 2

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The rules don't provide strict limitations to distance, DC or any other conditions to succeed the check. They are supposed to be described in the adventure itself, or set by the DM.

There are suggested checks in the LMoP which specify distance explicitly:

Spotting a secret door from a distance of no more than 10 feet without actively searching for it requires a passive Wisdom (Perception) score of 15 or higher

But in this case it's up to the DM to set the distance. It is reasonable to make the check before the attack, to justify surprise.

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Encounter distance is up to the DM but there are a number of rules related to Perception you may have missed.

In my case, once the party was quite close to the ambush, I rolled the stealth for each goblin and 3 out of 4 came under 15, which was the passive Perception of our ranger, so the ranger noticed the goblins while others were surprised (nobody was actively looking).

Your procedure was largely as the adventure directs, and as the rules are intended to work. In Overview of Act I: 2. Goblin Ambush, you are directed to:

Check to see who, if anyone, is surprised. The party cannot surprise the goblins, but the goblins might surprise some or all the characters. Make a Dexterity (Stealth) check for the goblins, rolling once for all of them...Compare the result to the characters’ passive Wisdom (Perception) scores. Any character whose score is lower than the goblins’ check result is surprised and loses his or her turn during the first round of combat...

I would note the following, though:
(1) Generally, as a DM, you are supposed to select this encounter distance as you deem appropriate. However, in this case, the flavor text of the encounter says:

As you come around a bend, you spot two dead horses sprawled about fifty feet ahead of you, blocking the path.

The goblins are hiding on both sides of the path, between the party and the horses. No map is provided for the encounter, but we know that the goblins must be closer than fifty feet. In fact, if we assume that the two which enter melee combat can do so on their first round, they must be at 30 feet or closer, since this is the walking speed of a goblin. Since there are "dense thickets" on either side of the trail, the DM could even rule that these thickets are difficult terrain of the type the PHB calls "undergrowth" or "briar-choked forests". In this case, the goblins might start only 15 feet away!

(2) Given that the terrain in which the goblins are hiding is "dense thickets", a DM could also rule that the area is lightly obscured, of the type the PHB calls "moderate foliage". In this case, the PC's would have had disadvantage on their Perception checks, which means your ranger's Passive Perception would have been 10, not 15. I would not recommend this for novice players, though, as it would give a considerable advantage to the goblins and likely enable them all to attack a party in which every PC was surprised the first round.

(3) If the ranger's Passive Perception beat the Stealth rolls of three of the four goblins, then the ranger noticed three of the goblins, but could still have been surprised by the fourth.

(4) While you say that nobody in the party was actively looking, you should be assuming that adventurers are always on the lookout for danger, unless they tell you specifically that they are focusing on something so demanding of their attention it would preclude them from doing so. See the PHB section on Noticing Threats.

I also took the approach that once either side notices the other and they aren't sneaking, combat starts (provided the creatures are hostile), so once the ranger noticed the goblins the combat was on and everybody rolled initiative.

Yes, this is correct.

However, is there a limit to passive perception, or does it extend to the edge of normal vision? So if a character is walking in broad daylight, can they spot a goblin ambush from, for example, 300 ft away, or is it up to me as a DM to determine if they have to be, say 50 ft from the ambush to notice? Likewise, would the goblins see the players advancing down the road from hundreds of feet away?

As previously stated, the adventure stipulates that the encounter starts with the party at fifty feet from the horses, and furthermore says explicitly that "The party cannot surprise the goblins," so indeed they have been spotted at a great enough distance for the goblins to ready their ambush before the party's arrival.

(5) However, in general your Perception would extend at least to the limits of your vision, and possibly beyond if you could hear farther than you could see. Of Perception checks, the PHB says:

Your Wisdom (Perception) check lets you spot, hear, or otherwise detect the presence of something. It measures your general awareness of your surroundings and the keenness of your senses.

Thus it is up to the DM to decide what counts as your "surroundings" for any given encounter, taking into account your senses, as well as the lighting and anything that might obstruct vision. However, the standard assumption in 5e is that the characters will know the location of any creature 'on the board' that is not Hiding.

If I were to rely on my guts, I would say that the goblins can see the players coming down the road (no chance of hiding in plain sight), and would attack when the players are within 80 ft (normal range of their shortbow), while players would have no chance of spotting goblins hiding in the bushes, but this would mean the players would always be surprised, which I think would unfairly disadvantage people who have invested in Wisdom/Perception.

Given the terrain the party is approaching through and the fact that they are traveling in a wagon, it is a safe assumption that the goblins have spotted them from a long way off. And yes, "no Hiding in plain sight" is a rule. The characters definitely should have a chance of spotting the goblins - as you intuit, this is what the Perception skill is for. As far as when the goblins would attack, if the adventure were not prescribing their tactics, then yes, as soon as they had line of sight on the characters and normal range with their bows makes sense. They would try to avoid melee if possible, Hide after every attack, and move a square or two while Hidden if possible.

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