D&D General Dragon Spells?

[MonsterEnvy]

Darkness is always a good spell for an Adult Black. Fits them too.

 

[MechaTarrasque]

The thing with 5e (and I am assuming One DnD) is that if the monster is using spells of the same level that the PC's can cast, it is probably not going to increase their offense CR. The main reason to do so is if the monster lacks a ranged attack (not a problem for dragons). So, for a 5th level party, let the dragon cast fireball while it is waiting for its breath weapon to recharge. If your party is clumped together while fighting a dragon, they deserve what comes next. If the dragon can only catch one PC with a fireball, it will probably better off trying a bite and a couple of claw attacks. I would be reluctant to let the dragon cast higher level spells than the PC's can; that is fine for a lich but not so much for a dragon.

I usually give this advice for fiends, but I think it is okay for dragons: I am 90% certain warlock is really the way it is so that it is easy to add a couple of levels to a fiend (or a dragon). Range attack and a couple of spells, and invocations are good for some sneaky options. Pact of the Chain seems like a good one for dragons....

 

[RoughCoronet0]

I give dragons spells or spell-like abilities based off a few factors such as their species, environment, classes, personality, and ambitions. For example I have a Young White dragon NPC that is both the protector of a gnome village and the owner of a very popular tavern frequented by people who travel between the three major kingdoms of the northern part of the continent. She is technically half red dragon but doesn't show many sights of that side of her heritage. Her spell list has a mix of fire and ice spells (for her mixed heritage), spells like unseen servant, prestidigitation, animate objects, and calm emotions to help with maintaining her tavern, and a few illusion spells she has picked up from the gnomes she protects.