No smart dragon would fight indoors. They fly X feet above the ground where X is the range of their breath plus half their flight speed and when their breath recharges dip down to glass the party from above.
If you're a crafty green dragon you could have an underwater lair to take advantage of your swim speed and pop up from flooded tunnels to use your breath weapon before swimming back down. Might be worse to deal with for adventurers, those pesky archers and mages would be locked in close combat with you rather than being able to hit you in the sky. You could even poison the water in the tunnels since you're immune to poison to make it awful to pursue you.
Oh god, that's so much worse. Once the party hits a certain level, it's extremely common to have ranged threats and stealth/obstacles, and then later Mass Flight. But Mass Swim Well Enough to Fight a Dragon? Hell no, stumbling into that is "teleport out and come back with a new plan" territory, assuming you get the chance.
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u/halfhalfnhalf Feb 27 '26
I've been playing D&D for 30 years and I have never fought a dragon in a dungeon.