The dragon’s lair appears to be magically warded with a haze that zaps any who enter it or who use certain magical powers from within it.
There are also mushrooms present. Some that create clouds of concealment and some that attack with spores.
You defeat the remaining troglodytes but are unable to do much damage to the dragon. The dragon allows you to leave with your lives as it seems to have no interest in continuing the battle and risking its treasure.
You leave Hammerfast and rejoin Ourun who has been joined by two dwarves from Anvil, over the mountains. There is Gimlan, and female dwarven warrior, and Finnick, a male dwarven sage. Finnick suggests a plan to kill the dragon now that you know that it is a purple dragon. He suggests that he creates a teleportation circle and that the party lure the dragon into it and be teleported away from Hammerfast to El Shalal. He believes that the sun will kill the dragon in less than a minute. He will need two weeks to return to Anvil and gather the components and the ritual to make the portal.
You decide that during the two weeks you will go back to Five League House and find news.