Ancient Copper Dragon Spellcasting

[Kadesh]

Players have come across an Ancient Copper Dragon, who is currently setting them quests, but as they are getting more powerful, i'm thinking of having it get more serious as it realises that of its vassals, they are the more capable. This will culminate in a Showdown with the Dragon as it tests them in combat in preparation for a to yet be decided unknown task.

What spells would a CR21 Ancient Copper likely have? This is for vsing a party who will likely be level 13-15.

One spell it has to have is Crown of Stars, because I have given a scroll of it to the party saying he crafted it himself, but other than that, I am open to suggestions. I don't particicularly want to go for the obvious power options of Counterspell, and Shield, also because of the Slowing Breath making things doubly hard, and no healing.

For reference any spell that is 7th or lower is available for suggestion. Going for more theme than power.

Thanks!

[Whyrocknodie]

Have the dragon use spells that reflect the as yet unknown task it wants them to perform. That way it's like a field test.

For example, if they are plunging into the Frozen Abyss of Ur'Thelgurzz then ice storms, spike growths and hungering pits of soul-numbing blackness should be the way to go.

[CTurbo]

I think it would be cool to give it the Paladin's entire spell list. MAYBE Cleric

I like the idea of an Ancient good dragon having a Divine spell list

[Segev]

In prior editions, at least, copper dragons were known for being tricksters and fond of riddles and puzzles. I suggest simulacrum and project image for his list; the latter gives him at least once per day the ability to communicate at a distance of up to 500 miles.

[KillingTime]

I'd actually suggest giving it the Bard spell list given their nature.

[Kadesh]

I'd actually suggest giving it the Bard spell list given their nature.

They have all spell lists to choose from, but the fluff suggests they learn spells, so have 4 spells known.

I think Simulacrum falls under the 'too powerful' nature. Project Image works, certainly, but it's not something I see as something the Dragon would want: even though it can sense through the Image, it also makes it hard for the Dragon to know when to contact, short term of throwing further divinations on it.

That said, I think I've decided.

I think Bones of the Earth is a good one, as it keeps flavour without being too dangerous, or inhibiting (like Wall of Stone may be), while providing further difficult terrain.

Another one is Divine Word, to represent a powerful roar, while the last is Erupting Earth: that's a 7d12 Dex Save and Difficult Terrain.

Between everything causing difficult terrain, and wing blasts knock backs/maneuvers it should be a pretty difficult fight without being outright 'you do nothing this turn' unless it flies/fom (note to self, hand out a little potion of that and a feather token).