Secret Organization's Second Mission

Black Shadow, who you've never seen before, starts talking to you... Who could this be?

Black Shadow introduces himself as a member of the Secret Organization, then thanks you for doing a good job on the first mission. Now, he needs you to do something else. Your second mission is to eliminate the Decaying Coolie Zombies at the Forest of the Dead, collect the Decaying Zombie Molars, deliver them to Shammos, and take what he gives you in return...

You can enter the Forest of the Dead from the open door located at the right side of the bottom floor of the Chief's Residence.

When you gave the Decaying Zombie Molars to Shammos, he gave you one Black Key, then laughed eerily.