Surprise! A DMs Guide to Judging Ambushes

I THINK THAT EACH AND every DM has one stupid problem that goes undetected for years, well, at least 1, honestly we all probably have many, but there is usually at least one, that when you find out about it then it makes you feel really dumb.

My problem was the Surprise Roll. I just never understood it! I don’t know if it just wasn’t described clearly enough in my books, or just what the problem was, but I did it incorrectly for years. Today’s post is about Ambushes, and how to run them fairly, but of course the biggest element of an ambush is that the ambusher gain the element of surprise.

Surprise Rolls

To check for surprise, we as the DM, have to first determine a number of factors. First we have to figure out how far away the monster is, and second, we have to roll a 1d10, an unmodified check is 1-3 on a 1d10, thus surprise happens less then half of the time, when enemies bump into each other, but some creatures have a bonus, or a penalty to their surprise roll.

Lets take a gator as an example: Alligator’s are masters of ambushing. They pick lairs where it is easy to hide, typically swamp water with lots of cover. They always impose a –4 to surprise rolls, This means that the gator can surprise the PC on a roll of 7 or below. At the same time, alligators are very hard to surprise, the average person is incapable of such a feet! We know this because the gator’s –4 also works in its favor, and is used to determine if the adventurer surprises it, thus even if we roll a 1 on our surprise roll (1d10) the gator still isn’t going to be surprised.

There are, of course, modifiers such as being invisible, or what the weather is doing, which you can find in the DMG. Being suspicious helps a bit, but you have to be suspicious of a specific spot in order to benefit from the bonus.

A major factor in gaining surprise is DEX. Those with high Dexterity are much harder to surprise, and it may be impossible for them to be (DEX of 18 are only surprised on a 1), while those with low DEX scores are very very easy (DEX of 3 are always surprised on a 1-6).


Surprised characters get no attacks for one round. They are totally off guard and vulnerable. They get no AC bonus for high DEX, and their attacker also gains a +1 to hit them!

The attacker can’t cast spells, but some monsters can use spell-like abilities, and the surprised persons all suffer a penalty to their saving throws, thus a monster like a Medusa could really do some damage to a party, all of the opponents didn’t expect her to be there, and their odds of stupidly looking at her dead on is very high!

We, as Dungeon Masters, must also consider what we can let the players and the monster get away with. This is a judgment call! And it probably will depend on the situation, but I know that I personally allow the use of magical treasure. Say, a wizard has a wand; I go ahead and let him use it, but this also means that I let monsters have full attacks, and what one can do, so can the other; so enemy wizards with wands of their own get to use them as well, of course assuming that the casting time is instantaneous.


Gaining a surprise is a definite element to properly ambushing other parties, but the difference is that ambushes aren’t determined randomly, these are always set up before hand, and it is totally up to you, as a DM, to decide if they are successful or not!

Of course this should work fairly consistently, PC characters can set up an ambush just as easily as enemy NPCs, so it will always be a judgment call as to if they are successful or not.

Advanced Dungeons & Dragons: 2nd Edition actually has two different rules for ambushes. The original 2e method (the PHB with the warrior on the horse) says that ambushes are exactly the same as surprises, and are handled in that method, including the surprise roll at the beginning of the encounter. But, when it came time to reprint the books (the Black PHB with the warrior busting the door down), they changed this to a different method which I think works much better.

Ambushes give the attacker a bonus round of attacks, then surprise is checked, then the combat is ran normally.

Let’s make an example: The PCs are following a well used road, but are about to be ambushed by bandits.
There are 8 archers hiding in the woods, and 4 fighters pretending to be tired woodsmen walking towards the players. The players can see the woodsmen but not the archers, but the plan is that once the PCs are in range, the archers are going to fire at them, the woodsman are going to yell “Bandits!” and run towards the party and appear to be joining them for everybody’s mutual protection, however once they get within melee range, they will be attacking as well.

This is a multi-layered ambush, and it will work because we said so. (We are Dungeon Masters, hear us roar!) Thus, the archers get a free attack, all of them can shoot two arrows at the PC’s before the second wave hits them, after firing their weapons, they’ll drop them and grab their swords.

About this time, the PC’s learn that the woodsmen are enemies, and they, the woodsmen, get a free attack! Now we check for surprise. There are over 10 members in the enemy party, so that is a +1 to the favor of the PC’s (surprised on a 1 or a 2). But, the enemy was camouflaged, pretending to be something that they weren’t, -1 to -3 depending on how the PC’s reacted to it, lets say, to avoid arguments, that we totally snowed the players, and the attackers get a +3 (Surprised on 1, 2, 3, 4, or 5), however, the party is now aware of their folly, and are either panicking or ready for an attack, again judging their reactions as players. If they are panicking they are in trouble! (Surprise on a roll of 7 or less) but if they are ready, they get a –2 (Surprise on 3 or below).

Characters with High Dex can deduct their bonus from the Surprise Roll, thus a roll of 3 will still surprise their peers, but not them, they get to roll initiative and attack that round, but for everybody who is surprised, the ambushers get another free round to attack! The woodsmen attack first, and then the archers armed with swords join the melee and also get a free attack before any initiative is ever rolled.


An effective ambush also changes a few other rules. An ambushing wizard can cast spells. They are ready, and as long as they know that an enemy is approaching, and when they will be within range, they can go ahead and attempt to cast. They may have to pass a WIS check to do it! But they can still attempt to try, and the opponents saving-throw will be modified in the spell casters favor, receiving no bonuses for DEX and imposing the appropriate amount for surprise.

The first attack of an ambush will be done with an automatic +1 bonus to hit, ignoring AC bonuses for high DEX, and continues if the party is still surprised on the following round. Now keep in mind that depending on the time of day, and what the adventurers were doing all day, they might not be wearing their armors at all either! Won't that be fun?


Naturally, forethought is needed to make an ambush work, and it might not! It is completely up to the DM. Characters may get mad and claim bizarre things to try and weasel their way out of the effects, but we have to plan for this too. Thus, in order to make a successful ambush, it is probably best if we don’t give them any reason to suspect anything, or add some form of misdirection so that the players themselves fall for it. If the party has been fighting goblins all day, then the chances of them falling for an ambush could be so slim that they won’t fall for it. But we can trick them into it, say by having 3 goblins act as bait: The players see them, and if they give chase, they round the corner and are surprised by 10 goblin archers who pepper them with arrows. But what we have to ask ourselves, as DM, is: Is this truly an ambush, or is it just catching the party by surprise? Depending on the situation, we may get different answers for this. If this was planned by the goblins, then it is an ambush, but if these 3 goblins just happened to turn the corner and warn the others that they are being followed, then it could just be a surprise. The goblins don’t really have any plan set up, now if they had set up a trap and given this encounter some forethought, THEN we have the elements of an ambush.

Thankfully there aren’t too many rules which dictates what is what, thus the over-all decision is ours to make. Granted, we don’t want to use ambushes every game, else they will lose their impact when we do plan them! But we also want to make them beneficial to whoever is pulling it off. Players can also utilize ambushes, but we need to judge when it will work, when it won’t, and if it really is an ambush or simply catching an opponent off guard.

ART By: Jeff Easley


Timeshadows said...

I wanted you to know that both Surprise and Ambush went very well in my Basic Fantasy RPG-inspired playtest game today/tonight -- because of your 2e article.

Thank you very much.

RipperX said...

Thanks for that awesome feedback, Timeshadows! I am honored to be of service.

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