D&D 5E Help Me Build a Challenging Dragon Mini Boss

[Retreater]

My 5th level party is preparing to run into a green dragon laired in the ruins of an elven city. The party consists of a paladin, monk, ranger, wizard, and cleric. This is sort of the lieutenant under the BBEG of this portion of the campaign (think the Horned King from "The Black Cauldron.")
Anyway, I'm wanting something memorable and challenging, but I think the CR 7 green dragon in the Monster Manual won't work - it will do too much damage too quickly with the breath weapon, but will otherwise not be able to hit or damage the party enough. Really the breath weapon seems to be the only reliable attack, and it's damage potential is too high.
Does anyone have any suggestions about a better version of a 5E dragon? Or a similar monster I can re-skin?
Thanks!

 

[DND_Reborn]

First, love the movie reference!

We had a very similar mini boss in our campaign at 5th level when we were playing RAW. Here is the trick: if the party suspects it will be facing a green dragon, make it black instead!

Our battle was incredible and we won, but barely and that acid was a SHOCK! We thought we were facing a green and prepped for poison damage. Anyway, the line of acid is less likely to hit many characters 2 or 3 at best and is resisted with a DEX save, which is maybe a bit better for your group than the CON save? (you would know better than I...).

Of course, a CR 7 or 8, tackled in its lair (remember, it can breath underwater and should fight the characters near a source of water to use tactically and to escape into if needed), should possibly be a TPK. I would be VERY cautious.

You might want to switch it to a Wyvern or something CR 6. With the poison stinger, it can still be a challenge in the right set up. I don't know how much leeway you have here considering what knowledge the party already has.

 

[Leatherhead]

Do you mean the CR 8 Green Dragon? Because that thing has a Multiattack which averages more single target damage than it's breath weapon does, with 44 DPR. And sporting +7 accuracy it has a legitimate chance of taking out your typical level 5 Fighter in one round. Did you somehow get it mixed up with a different Dragon?

Actually, maybe the better question is "What are your group's stats?" if such a beast doesn't have a decent chance of clawing them to death.

 

[Paul Farquhar]

The CR4 Thesselhydra from the Stranger Things set sounds like the sort of thing you want.

 

[Imaculata]

The trick to building any challenging dragon encounter, is minions combined with an exciting terrain to fight in. The dragon can have young dragons, which (though much smaller) can still cause quite some damage.

The dragon may have a dangerous multi-attack, but a dragon would probably be smart enough not to get into close combat, unless it feels it can safely do so. Since the dragon's breathweapon is such a big threat to the players, you can design the terrain in such a way that there are spots for the players to take cover. You can also think about whether the players have a means to force the dragon to the ground. Maybe it only comes into close combat if the players threaten its young?

 

[Paul Farquhar]

Here is a suggestion. Take a wyvern. Apply the half-dragon template (this should make it CR 8). Give it two legendary actions (bite or tail attack).

It should be beatable (with difficulty) by a 5th level party - and it's not very bright, so it's tactics may be a bit off.

This way you don't "spoil" dragons by throwing in a weak one.

Also, if the party know what they are going to be facing (e.g. poison damage) they can prepare countermeasures (e.g. Protection from Poison spell).

 

[Draegn]

Being worried about the breath weapon, you could have the poor darling dragon injured in some manner that prevents it from using it. The players could then befriend it and heal the injury thereby turning a foe into an ally.

 

[Umbran]

I read the thread title at first as "Help me build a changeling dragon mini boss."

This is not of use to you, but I hope someone likes the image as much as I do...

 

[Retreater]

Do you think it would be ok (not game breaking) to handle the breath weapon attack this way...
You automatically take half the damage on the first turn you're hit with the poison cone. Then the next round you save to avoid the other half. This way it spreads the damage between two rounds, gives a chance for healing/buffs to avoid poison/etc.
I'm most concerned about 42 damage from the breath attack. (I nearly TPKed the same group with a black dragon a few months back.)

 

[iserith]

I actually think your 5th-level party will do just fine. By the numbers, that's just a Hard encounter and this monster is in LMoP against (usually) 3rd- or 4th-level parties. Plenty of people have reported that they've succeeded in that fight. A Hard encounter versus 5th-level PCs is almost certainly going to go the PCs' way in my experience, especially if they have time to prepare. The cleric could hit every person in the party with protection from poison, still have enough slots for bless, and this dragon will likely be a pushover.

As with anything, I recommend telegraphing the green dragon's abilities including its lair actions prior to the PCs encountering it. This will give them an opportunity to prepare and, whether they do prepare or not, removes the perception of any "gotchas" if things do go badly for them.

I would likely spend the most amount of prep time on building the lair, which would be along the lines the Monster Manual suggests - a maze of brambles choked with fog at the center of which is a sheer cliff in the side of which is a cave. I might even do a "false" cave - a smaller dug-out area about the shape of a, say, 30-foot cone into which the green dragon throws some of its treasure in plain sight - only the "gold" it puts there are wooden chips painted to look like gold. If it detects someone climbing into there, it swoops down from its real lair some 60 feet above, blasts the area with poison breath, then seals them inside with a wall of thorns (lair action) while its breath weapon recharges.

If there is an elf in the party, that character gets the brunt of any melee attacks until the PC is unconscious at which point the dragon grabs the body and flies away to be used as a hostage in exchange for gold. The dragon is a manipulative creature, after all. It won't honor any bargain and plans on eating the elf after the PCs supplicate themselves. I'd probably give it some spells to include charm person which it may use on the ranger. That'd be a useful servant for a green dragon.

Prior to all that though, I'm going to play up some kind of creepy exploration challenge in the forest around its lair, where the PCs run a big risk of getting lost and bad things happening.