Prontera Crypts NPC can be found north of Prontera outside of the Prontera Castle (prontera 159, 330)

Prontera Crypts is a guild dungeon. Your guild must be level ten with at least 10 members in the guild. (You do not need 10 members in your party to enter the crypts.)

Kill the MVPs (5+) to spawn the final MVP, Pori Jr.