Dubas is an NPC.
Dubus is located in the Arena. He gives you the Search for Legendary Mine Quest. After you completed his quest, he'll either reward you with 5 Blue Crystal which you can use to exchange with Bead Boy. Or you failed to obtain the chest he wants, you get an Ancient Document which you can promptly exchanged with the Archaeologist who is also located in the Arena. The Archaeologist will reward you with 0-3 Blue Crystal.