Dungeon: Twilight: Vol. 4: The End of Dungeon — Joann Sfar

The last two stories of Dungeon!
 

In High Septentrion, there has been a violent eruption on the planet of Terra Amata. It's a scramble to find breathable air, but the wizened blind, mystical dragon the Dust King (Marvin) thinks that it is perhaps time for him to die heroically. However the feisty young Marvin the Red refuses to give up and plans to find a way out of this mess, including finding a way to actually breathe… Art by Alfred of Why I Killed Peter.
 

And in The End of Dungeon the more the islets of the planet Terra Amata move upward, the less there is of breathable oxygen. While Marvin the Red and Zakutu, daughter of the Grand Khân, attempt to protect the seven objects of Destiny, Herbert and the Dust King are forced to swear allegiance to the Dark Entity in order to gain access to breathable air. 
 

All things must come to an end and so it is with the great Dungeon.