This no longer a young gold dragon.

Yeah, like I said, I wanted something between a Young Gold Dragon and an Adult Gold Dragon. 

The problem is that the party does simply absurd amounts of damage. On overage, even with only the ranged characters, the Dragon will be dead in about 2-3 rounds. They have a decked out Arcane Archer (the aforementioned fire-immune Fighter), who could kill the dragon in one round if he gets Haste (from the party Wizard), burns Action Surge, and rolls average or better. Add to this a Warlock, a Wizard, a Bard, and at least some ranged options for the Monk, Paladin, and Rogue. 

I didn't just want to increase his defenses to be able to soak the Arcane Archer, because then everyone else in the party suffers. So, I tried to figure out how to let him do more in the couple rounds he would have alive. 

You're right about the ancillary Haste effects, though. I wasn't considering them. I was only thinking about the extra action. I might have to drop that. 

Will do! Wish me (or, rather, my party) luck!

Maybe change up the Dragon.  Give it an item that changes its breath weapon from fire to cold.  Also give a few minions that can also side track some players so they are all not focused on the dragon at the same time.  Lair effects Lair Effects Lair Effects.  Most dragons are very intelligent so have it attack the spell caster who casted Haste because that will take out the person who had the spell cast on them for one round.  Also target the healer.

I'll apologize in advance for not reading all responses, so this may be repeated info. I grew up with my dad (veteran AD&D DM) teaching me all of the evil tactics he would enploy, specifically to dragons. I'll also apologize if some of my info is spotty or a bit inaccurate as I have not researched the creatures of 5e as much as AD&D

-Dragons use to have a natural polymorph (like druid Wild Shape). If they don't have that, use some natural spellcasting to polymorph. In lairs with low visibility or massive elevation changes like cliffs, a human can be much harder to fight than an ancient dragon, especially when they are firing spells from concealment or far out of most spells/melee.

-Dragons have breath weapons and flying. WHY NOT USE THEM TOGETHER?! Silver Dragons are regarded as the righteous knights of dragons and states they will strafe with a breath, then land for melee. Why? Because it kills/debilitates the enemy before close engagement.

-Dragons older than adolescent will typically gather minions or thralls. The most unrealistic thing to see is a dragon on the city-threatening scale who just flies around solo in open ground with no protection or extra insurance.

That's just the tip of my strategic iceberg. Awesome stuff so far, keep those PCs on their toes and show them why a dragon, even a young one, should be fought with nothing short of life-threatening apprehension.

I think the issue with newer / younger players is they think D&D is like Skyrim. after one breath attack the dragon will land and try to fight them, and when you fight the dragons fight of flying  60-120 feet and nuking the party they cry that you're being unfair.  

Quote from Estoy_Awesome >>

I think the issue with newer / younger players is they think D&D is like Skyrim. after one breath attack the dragon will land and try to fight them, and when you fight the dragons fight of flying  60-120 feet and nuking the party they cry that you're being unfair.  

All monsters should be run just as intelligently.  It makes me sad when they don't use tactics.

One thing Iearned about dragons came from seeing the ones in Guild Wars 2. 

Dragons there are the big bads of the setting, and are really nasty.   The black one basically had commands of undead hoards, and we're not just talking zombies.  We're looking at some rather nasty undead creations that can do a wide variety of things.  Vecna, eat your heart out.   

The green one?  Archdruid mixed with a bard's illusions and enchantments.  Its poison came in the form of messing with your head as well as the very ground you walked on.  Going into a forest after one was tricky, because that forest turned into a trap riddled maze, combined with the equivalent of evil dryads that can charm you.  

The red one lived in freaking lava.   Its common knowledge that reds live in volcanoes.  Its also common knowledge that fire elementals (not just the elemental critters, but everything fire themed from that plane, including djinn and more) show up around there, and that its best not to use fire magic.  Combine all that.  The bare minimum needed to fight a red dragon is being able to survive in its lair of molten rock; it can use a lair action to cause a magma geyser, sure, but think about it.  Its lair is filled with magma EVERYWHERE.  Its scales should be covered in still cooling magma.  

Haven't quite seen the blue, white or "sea dragon" yet, though that will change for blue soon enough.  And I'm betting the sea dragon's going to be a combination of a dragon turtle, kracken, and mind flayer, but those leviathans are different than D&D's dragons.

Quote from Mephista >>

All monsters should be run just as intelligently as this.

Quote from Mephista >>

 

Haven't quite seen the blue, white or "sea dragon" yet, though that will change for blue soon enough.  And I'm betting the sea dragon's going to be a combination of a dragon turtle, kracken, and mind flayer, but those leviathans are different than D&D's dragons.

Remember. White Dragons are super dumb and animalisitic compared to the others.

The Ancient White is Int 10, an Adult is Int 8... and they go down from there.

Whites are Super Predators, but really not very bright.

Whites are the dumb orcs of dragons.  That said?  INT scores have nothing to do with tactics.  INT is basically the skill for academics and identifying things - magic, cults, objects and ruins.  Some traps.  Sure, they might suck at long term strategy and logistics, so I'd never make one a general or master chess player, but in terms of common sense and short term tactics?  Not a problem.

Good points to the above. Whites may not have the intellect to fashion complex illusionary scenarios, but they may use them similar to an angler fish and try to lure adventurers or prey. If they aren't taking that approach, I feel like they would try to use natural terrain to their advantage: cliffs, wide tundras, weak snowbanks (walk, walk, drop!), etc. Animals won't be able to manage armies or create the most intricate lairs, but they can be insanely crafty while hunting and can potentially draw a few lesser creatures through mutually benefitial relationships.

I disagree with you.  Int isn't just academic learning it's cognitive processing power.  That's why it's connected to all skills of remembering things.

Whites are Animal Smart not People Smart, except the really old ones.

Int 10 is "average human"

Int 8 is "below average human"

A gorilla is int 7.

Dolphins and monkeys are in 6.

Now there is a case for arguing of the numbers feel incorrect.  I personally think a dog should be higher then it is (3).

But given this scale an Adult White is equivalent to a human with below average IQ.

Quote from FullMetalBunny >>

I disagree with you.  Int isn't just academic learning it's cognitive processing power.  That's why it's connected to all skills of remembering things.

Whites are Animal Smart not People Smart, except the really old ones.

*shrugs*  Whites are still sapient beings, whereas most beasts are not.  

As for INT being cognative processing power, well, apparently Medicine is apparently a WIS skill.  There's going to be exceptions to that rule.

But whatever, to each their own game.

Even with a low intelligence, dragons as a whole are apex predators with beyond animalistic intelligence. Some species may be able to discuss the philophies of life and multiverses, while others can barely hold a conversation past what's for dinner.

Regardless of their cognitive aptitude, they possess enough know-how to take their environments and turn them into utter deathtraps for even cautious or seasoned adventurers. The only variable to the danger of their lairs and general habitats is how long they have been able to adapt it to their needs (generally relative to age). A new dragon on the block would have rudimentary defensive measures compared to one that has been around for centuries.

I recently ran a Young Blank Dragon encounter at the end of a module.  Basically the final encounter of the adventure.  I really challenged the party and had a few of them go to zero HP a few times.  Eventually they whittled her down to the point where she decided to flee.  My idea was I would have her flee and become a recurring story arc foe in the campaign. 

My party become very frustrated and let down.  They felt they should have finished her off, and honestly they would of if I didn't end it with the dragon fleeing.  I later talked to some of the players and they felt they didn't have any options against her because they were melee and she stayed in the water with 3/4 cover and sometimes full cover.  I hinted they could go in the water and face her, albeit to some disadvantage. Mostly, the characters ran around getting hit with acid breath, and healing each other, while one player damaged her with magic.

So the issue was two-fold.  Some players felt they had no options in the encounter, and even when the casters managed to get her near death, they were upset they couldn't finish her.

I guess I am looking for advice on how I could have made this encounter more enjoyable. Also I am looking for opinions on if I should have let them finish her off, or stick to my grounds of creating a campaign villain.

My opinion is that having a villain, especially a dragon, get away is a great story arc. It is disappointing because we are so used to getting a win, but that's why next time they go up against this particular villain it will be that much more satisfying to defeat them. 

100% onboard for fleeing villains as long as it's not railroaded. 

I have the feeling that players are not often disappointed when an enemy flees, but more when a challenge suddenly ends with no conclusion.

When a Big Bad (tm) decides to scamper off, consider exchanging the ongoing challenge (the battle) with another (ideally in stride).

"My trusted lieutenant, stay here and give your life for me, will you?" (exchange with another focus of the battle. Works best when this doesn't come from nowhere, but was previously hinted)
or
"The dragon, seeing his perfect plan going up in flames, shifts all his weight and crushes on the central pillar. The entire cave begins to shake and debris starts falling. The dragon doesn't seem to care much about most of it, but if you don't find your way out of here quickly, you'll be crushed." (divert with another challenge)

Depending on the group, you can also try other avenues, such as bargaining (usually for information), blackmailing ("kill me and my prisoners die of starvation, you'll never find then in time"), etc.

That said, the Big Bad usually has some means to escape - good information gathering might hint such means to a well-prepared group so they can prepare in advance. "The dragon has another exit from his lair. Let's put a few net traps there before we enter the caves", or "The vampire will turn into mist when he's defeated, and leave. What can we do to stop it?" or even "the succubus is heard to just vanish in thin air when seriously threatened. How can we stop her from just escaping?"

As for options, those are usually the DM's duty to consider. You might want to allow more avenues of approach for beginner players, or even hint towards things "The dragon dove under water, but there are a lot of stalactites hanging above". For more experienced players, or groups of 10+ level that include spellcasters, you'll find you need to do that much more rarely - players have a tendency to surprise you with out-of-nowhere brilliant tactics (and occasionally face-palming silliness, but it's part of the game too :p ).

The only thing you need to do in both cases is to keep an open mind about what they suggest. If they try to toss a few pints of oil from their lanterns on the lake, then set it on fire when the dragon emerges? That's brilliant. Let it work, rather than say "the dragon just emerges from over there instead". If the players surprise you, they can definitely surprise a Big Bad.

I hope that helps.

PS1. This underwater dragon encounter seems familiar...
PS2. Necromancer, eh? :p You could have made that post as a new thread and no one would bat an eye.