There's a few Easter Eggs that aren't very obvious to the player. One, get the flags from Shia's bedroom and two, get the crown from the puppet. When you see Terry with a shotgun, give him the crown after your conversation with him.

When you enter the last phase of the dungeon, to the left of the screen of the moloch statue is a hole. Use the flag from Shia's room to attach it to the statue and go down into the hole for another easter egg