How about a “PyroGhost”. It's a small ghost, colored red, the size of a watermelon, no arms, no legs, only eyes and a grin in a burning aura. He's not agressive, but easily scared, and likes to make people scream. The problem is, each time he appears in a room, his aura burns the object in contact with; it starts with little smoke, a burning smell, and then a small fire if nothing is done.
He took a building made of six appartments, as a home. The building has three floors, with two appartments made side by side on each level, connected to a stairs. From left to right, down to above, appartment #1 has zero resident, #2 has only one, #3 has three, #4 has zero, #5 has one and #6 has two. Each appartments have six rooms.
The residents are not happy and stay in their appartment to help the player; they walk to one room and wait before going to another, searching for any ghost activity. The ghost has a strange energy and the pke can only detect him when the player enters the same appartment where he is.
The ghost's actions are simple; he appears in one room, flies in it during a short moment and disapear. When a resident is in that room, the person screams and runs to the next appartment; he stays there a moment before returning home. Guided by the sound, the player will need to hurry to the right place if he wants to find the ghost. The player works alone in this mission but he has a partner outside in Ecto-1 who scans the place; with the radio, he tells the player if the ghost energy is stronger on the left or right part of the building, at this moment.
The player must also find the room where the ghost was to extinguish the object that may be on fire, using the slime tether. When returning home, the residents use their own fire extinguisher if the player was not there in time; leaving a trace telling that the ghost was here. If the fire reaches to other objects, the resident of the appartment will run outside, screaming at the player to do something about it.
The goal is to not let the place fall to a critical level to call the firefighters and trap the ghost.
When the player finds him, the ghost won't attack; he'll try to escape instead, flying rapidly around the room to confuse the player and make him miss. When the player holds him in the particle stream, he'll need to move the ghost outside the window, his partner will hold it after from outside. The player must then hurry outside to put the trap on ground, hold the ghost above it and capture it before he escape.
I think it can do a nice bonus stage in the game.
I don't know why but it was in my dream last night.