Dragon Encounters

Making dnd combat fun, finding monsters that fit together, monster tactics and strategies, and other ways of using the monsters of dungeons and dragons

ADULT BLUE DRAGON: Defenses Inside and Outside the Lair


Combat rating 19


1 Adult blue dragon (CR 16)

2 Air elementals (CR 5)

1 Earth elemental (CR 5)

1-2 Lamias (CR 4)


Combat rating 21


1 Adult blue dragon (CR 16)

2 Bulettes (CR 5)

3 Galeb duhr (CR 6)

1 Medusa (CR 6)


Combat rating 24


1 Adult blue dragon (CR 16)

1 Rakshasa (CR 13)

1 Archmage (CR 12)

1 Assassin (CR 8)

3-4 Gladiators (CR 5)


Combat rating 26


1 Adult blue dragon (CR 16)

2 Dao (CR 11)

3 Clay golems (CR 9)

1 Mummy lord (CR 15)

How to Use – Combat encounters (difficulty 18)

The blue dragon has quite a number of tactics he might employ against his enemies. Among them are:

Glass boulders: Glass is made by sand melting under extreme amounts of heat. Being struck by lightning will do it. Whether the dragon knows how to shape the sand into boulders, or whether he just breathes into the ground and digs any promising results out, he has a deadly arsenal at his disposal. It won’t be a small arsenal, either. The blue dragon excels at preparation.

While hurling a glass boulder might seem like poor tradeoff, a single attack when he could make three basic and three more legendary, it’s an attack that doesn’t expose the dragon to any form of retaliation. If the PCs are near a rockface, the dragon will be at the top, not near the edge, and will hurl the boulders over. If they’re in the open, the dragon will be in the sky, above the range of their bows and spells (he knows their range), dropping boulders onto them, one at a time.

Unlike normal boulders, it isn’t necessary for them to hit in order to do damage. Glass shatters, flinging its shards everywhere. It seems very logical to give the boulders 10-15 feet of range in every direction from the point of impact. This area of effect means that a single boulder could potentially hurt the entire party. It also means that the dragon doesn’t have to worry too much about aiming.

(Two quick facts that you may or may not know. 1) In modern warfare, the shrapnel that an explosion sends flying is as deadly or more so than the force of the explosion itself. That will be true regarding these glass shards as well.

2) Some people have the idea that desserts are full of sand. They picture this sand as being soft, like in a child’s sandbox. The reality is that desserts are as likely to be hard, dry earth and/or rocks as they are to be sand, and even when there is sand, long exposure to the heat of the sun renders the sand almost as hard as the soil. The point is that the sand will not cushion the boulder. Hitting the sand will break it.)

Ambush From Below: Another tactic that the dragon might use (and is straight out mentioned in the Monster Manual) is to cover itself with a layer of sand and rocks and hide in the soil. He can plot out where the adventurers are likely to go, based on the lay of the land, he can send out archers beforehand to shoot and run, thereby causing the players to climb over him without realizing it, and he can try multiple times until he gets lucky.

As the DM, you can even set up a scene where the dragon wasn’t actively hunting them, it was just taking a nap and the PCs didn’t realize.  

When they climb onto and over the dragon, they probably won’t realize it. Burrowing into the ground makes for excellent camouflage, and the dragon will lie perfectly still until he’s ready to rise.

When he rises, the party will be effectively split in two, with the dragon between them. Some of them may be knocked prone (have the PCs on the dragon’s back make a DEX save), giving the dragon advantage against them the first turn, and there might even be a PC who is stuck on the dragon’s back. (Once the dragon takes flight, it can get rid of the PC on its back quite easily.)

The dragon will probably take flight after 1-2 rounds, as this type of ambush only provides short term benefits. That said, the short-term benefits are good, allowing the dragon to do a decent amount of damage, and it should be able to retreat without significant difficulty, thanks to its wing attack legendary action.

Sinkholes: Also mentioned in the Monster Manual, which further suggests that the dragon uses treasure to bait the trap.

While treasure is a decent bait for the trap, so is the presence of the dragon itself. It would be quite in character for the dragon to land of the ground, or attack the from a cliff, knowing the as a result of its actions they’ll rush the dragon, and that there is a sinkhole present between itself and the party. In a similar manner, it can bait a trap by placing minions on the far side, especially minions with range attacks, and/or spellcasters.

There are two different ways that you can run a sinkhole: 1) As the PC enters the area and try to cross it, the sand begins to swirl down under his feet, as though falling through a funnel. There are three different measures of difficulty, depending on how far down you have him pulled.

1a) The PC is either pulled part of the way down, in which case he’s trapped by the sand and unable to move until someone throws him a rope. 1b) Depending on how deeply he’s stuck, he may be unable to move his hands also. This will both render him helpless to take most actions, and harder to rescue. 1c) He is completely pulled underground. Getting him out will require digging, and he’ll suffocate if stuck there too long. See the suffocation rules in the DMG.

2) The other way is to treat it like a pit trap. Say that the blue dragon carved walls out of the sand and covered them, exactly like a pit trap. There are two variants on this, which can make it a bit different than a normal pit trap.

2a) The trap was buried well, which means that a large amount of sand, rocks, and loose earth fell into the pit with the PC(s). While they shouldn’t need to be rescued from being buried, it might well mean that they’ll need to spend an action to pull themselves free. (Have them roll a DEX save to avoid being buried, or a STR check, where failure means they can’t just stand up, they can to dig themselves free.)

2b) The edges of the pit won’t be as well defined as they would be in a normal pit trap. As such, even after the pit is revealed, parts of the edges might fall away, or sand might start sliding in. Either of these can cause more PCs to fall into the pit. (These ones are probably not in danger of being buried, though.)

The Lair

The blue dragon’s lair will be high up on a cliffside, where the PCs can’t easily access it. (If it lets minions enter, it’s via rope ladder.) If they try climbing, the dragon will be able to take advantage of their position to attack them with its claws, tail, and lightning, all of which have far enough reach that they won’t be able to hit it back with attacks of opportunity.

Defending the Bridge: Once they are in its lair, I would have the entrance cavern be split in two by a long chasm, with only a narrow bridge letting people cross. (The dragon itself uses the bridge as a stepping stone. Dragons are obviously not scared of heights.) The narrow size means that only one PC can engage it in melee at a time, and they’ll have trouble switching positions, as the bridge has no railings. Since the bridge runs straight, the dragon can target its entire length with its breath weapon.

To prevent them jumping over, have the far side be at least slightly higher than the near side. In addition, if the ground near the pit is loose rubble and the ground is slanted toward the pit, there is a real possibility that jumping across will result in the ground sliding away under their feet and causing them to slide into the pit. The ground on the near side can be the same. This will make jumping off difficult, and allow the dragon to defend the bridge from either side, if it ever becomes necessary.

Defending the dragon from range attacks is going to have to be the job of the dust cloud from the lair actions. You can’t put to many obstacles near the dragon to give cover without restricting the dragon too much, given its huge size.

That said, the only part of the chasm the dragon actually needs it the area near the bridge, so if you leave 10-15 feet on either side of the bridge clear, the dragon can place multiple hanging rocks or spears to serve as artificial stalactites, reducing vision and give itself half-cover against attacks made over the rest of the chasm. (If you prefer beauty over realism, use actual stalactites. I suppose you could say that the dragon dislodged stalactites from elsewhere and set them in place where it wanted them.)

If they keep to the area behind the bridge, it will be easier to hit multiple targets with the dust cloud.

Collapsing ceiling: One other idea, mentioned by the Monster Manual, is a room where the dragon has the ceiling ready to collapse. Probably a weak glass ceiling, with loose earth piled up on the other side. (You could do this in the bridge room, but the sand from the roof will run off into the chasm. A different room would be ideal.)

When a piece of the roof collapses via lair action, the sand will start to run down, and any character with self-preservation instincts won’t want to stand beneath. I would suggest a round or two in which any creature underneath will get caught, as described in the lair action, then the sand will turn into impassible terrain (it was difficult as soon as the lair action was preformed) and then the players are informed that they only have another round or two until the ceiling collapses entirely.

(You can have multiple uses of the lair action cause the ceiling to weaken more, if you want to spin the story and make it seem more dramatic.)

If they don’t manage to defeat the dragon by the time the ceiling collapses, they’ll have to retreat, giving the dragon a chance to heal and then come at them again. (You’ll want to make a plan for this. It’s possible you can use an idea from above that you haven’t used yet, or adapt one of my ideas for the young blue dragon, the ancient blue dragon, or an entirely different dragon. Giving the dragon minions to bring with him, and/or having him catch them at a time when they’re less fresh, might also work.)

It’s also possible that the players will try to shore up the ceiling, which could earn them some time. (Although doing it while fighting a dragon is going to be impressive.) For its part, the dragon can always trigger more lair action collapses, as well as interfere with them shoring up the ceiling in other ways (depending on what they’re doing.)

Finally, it’s possible that the players won’t retreat and you’ll have to bring down the roof on them. In which case you’ll probably want to give them a chance to dig themselves out. Depending on what you think they can handle, you can have the dragon be waiting, ready to attack as soon as they stick a head out; you can have the dragon send some type of burrowing monsters in after them (D&D Beyond lets you filter monsters by movement type, among other things); or the dragon can assume that they’re dead and leave.


When a blue dragon uses minions, it will be to deplete its enemies’ strength, find out their abilities, and/or get them into a position that is disadvantageous to them. When its enemies are sufficiently weakened, it will strike in person for the killing blow. (Its ego demands that if the enemies are powerful enough to warrant its attention, it is the one to kill them.)

In battle, that means that you’ll want the minions to fight for several rounds before the dragon arrives, or before it intervenes. Once it does so, the minions will make ranged or melee attacks from the side, but they won’t occupy the center of the battlefield.

You can also use this as a story device. If the dragon is planning to kidnap a princess, or steal an artifact, it would very likely start by having its minions appear around the castle and launch multiple attacks at multiple targets. The aim of these attacks will be to draw the guards away from the real target. Once the guards are worn down and out of position, it will strike for the real target itself.

(This seems like a great way to begin a campaign to retrieve whatever it is that the dragon took. Perhaps give the players a clue as to the real target so that they arrive shortly before the dragon does. This way, you started with an exciting combat, introduced the villain, and gave the players incentive. They’re not going to like the fact that they didn’t manage to stop the dragon.)

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About Me

I have been a DM for several years, and I was designing home RPG games since my young childhood. I have been a fan of many different types of games (computer, board, RPG, and more) and have designed several for my own entertainment. This is my first attempt to produce game content for a wider audience.