Big Bad end boss

[tony gent]

Hi all I've just started running a campaign and I'm still unsure about the end boss.
I really want some kind of dragon but not sure what type , are there any dragons that have a affinity for gems above pure greed.
As the campaign revolves around a set of magical gem stones any thoughts

[lucky7]

Crystal Dragons from the Inner Sea World Guide come to mind. At CR 16, they might not be as tough as you're looking for, but they explicitly favor gemstones over coins.

[Rogar Valertis]

Try primal dragons. A crystal dragon could do perfectly for your needs. Or just put a primal dragon inside each of the gems (magma dragon for a ruby for example, a cloud dragon for a diamond and so on) and have the crystal dragon hire the PCs to recover all of the gems freeing its brethen... then you have a BBEG (big bad evil guy) and a few friends of comparable power for your PCs to face (maybe not right away), in this case I would make the number of gems the PCs need to recover equal to the number of PCs.

Edit: a great wyrm crystal dragon is CR18 and if you need tougher there's always the mythic template.

Btw, gems associated with elemental dragons could be:

-Azurite crystal (or aquamarine) for Brine Dragon
-Diamond (or sapphire) for Cloud Dragon
-Ruby (or fire agate) for Magma Dragon
-Onyx (or obsidian) for Umbral Dragon

[Vatras]

You can check out the Gem Dragons (there is a wiki entry with general info and a statblock on Planet AD&D) for ideas how to modify existing scalies, if you don't want the Crystal Dragon as is.

[Lincoln Hills]

Single-enemy fights can be somewhat anticlimactic. Supply the dragon with enslaved undead, constructs, or outsiders - or, if you're particularly wicked, a couple of simulacra of himself (the potential of getting stuck between two draconic full-attacks or within multiple breath weapon areas, even if one's half-power, is disheartening to say the least.)

[Dastis]

I enjoy the legendary rules from d and d 5th edition for any single foe boss fights

Rather than being a dragon it could be a spellcaster of another race using form of the dragon with a ring of continuation. Bonus points if he as a familiar he does the same thing with

Gem dragons from 3.5 MMII fit very nicely

Could just use a normal dragon that just loves gems/magic gems and nobody would bat an eyelash

There was an essoteric dragon template I remember where the dragon became so consumed by its hoard it slowly became part of it until the hoard was the dragon. I will post agian if I remember where this was. This type could gain stats/lifespan/whatever as it increases the value/magic/gemness/whatever of its hoard if you wanted an easy motivation