Here is a mini boss fight. Kill him, and close the portals. Killing him is simply a matter of wearing him down until he dies. The best way to do this is with your newest toy, but buy the frequency upgrade, or by using enhanced Boseo Darts. At this point in the game, if you haven't upgraded, you may as well get it over with. There isn't much else that you can do with the cash anyway. It won't impress Alyssia away from Venkmen. Don’t worry about getting lost. Do what you have to do and you can follow Ray to the next crypt. Follow it to the outside.
When Ray lets you lead again make your first right. When you encounter skull gates turn left, it's your only choice anyway. Straight ahead is a gate with two circular heads. Finally an open gate! Well, maybe not. As you get close a cult member steals one of these head keys. Now, you get to play fetch. Follow the cult member, and take care of him. Sadly, he won't have the key on him. Keep going until you reach a “T” shaped intersection. Head left, kill the other fiends and get the key. It’s too heavy to pick up so slime tether it straight down the path and to the gate. Before you can make it you will have to kill a big grave monster. Wear him down and eventually he will die. Get the key to the gate and it will open.