Just added a few pictures for those interested 

make a track to a door that leads outside. you can also call animal control to get it out of the house. 
 
i've had a squirrel or chipmunk problem. i was on the computer like always and my cat jumps into the window. i'm in the basement so the cats can come in with the window open. she drops the chipmunk right by the window. i start looking at it noticed it was alive. it ended up running in a corner. i thought i got it out the window. a few days later i hear squeaking noises. i find out the chipmunk is still in the basement. i got it out of the basement. we named him chippy.

Opossum. Guys. Opossum. 

Call animal control and they can use one of those long sticks with a noose on the end to grab it and take it out side. Or if it's not too long of a distance to the door make a...just call animal control. You will likely get rabies or have him bit off some round squishy part of your nether regions if you try to get him out yourself.
 
Or you could, make some possum stew. 

I mean.... an animal... trapped in a hot, enclosed area..... Maybe you should just throw in some curry sauce... add a little basil...

I hate to state the obvious, but I've dealt with similar issues before by just hustling it out with a broom.

Called animal control. 
 
"Just leave it, it'll leave at night time, leave the front door open" 
 
Cool, thank you sir.  
 
It's now disappeared up the chimney. Will update in a couple hours when it gets dark. 

I hear Helions are a good counter to a Possum rush.

for some reason i read the title as 'HOLY SHIT A GUYS FUCKING A POSSUM'
 
oh well.

so the possum played possum,great. Whatever you do, do not back it into a corner.

yo, where are these pics!?

Ha! Someone's afraid of dynamite.

" Things to do when Possum is in wood heater  Tell Giant Bomb Call animal control "

Eat it.

The same shit happened to me. I turned on my Xbox, and a possum was chilling right behind it. I had to guide its slow ass outside with a broomstick.

Things to do when Possum is in wood heater
 
Tell Giant Bomb
Call animal control

A wood heater?  You mean like a wood stove?  How does it not have a door on it?

One time I had a giant rat in my house. It was pretty funny, except when we found out there were like 12 babies and we had to drown them. 
 
It wasn't my decision.

You should wall off  your ramp. That always stops an early rush.

I read a thread almost exactly like this one on Neogaf.
 
Edit:found the thread
 http://www.neogaf.com/forum/showthread.php?t=401361

" Uh, call animal control. No reason to freak out. "

Collect vespene gas for the track. 
 
Video Ga... no wait that's wrong. Just make a wall of cardboard and whatever shit you have to make a track to the door. Line up one of the couches as a wall or something, just make sure he can't jump over anything and beat his ass out with a broom. 

Uh, call animal control. No reason to freak out.

Alright, I'm just gonna be plain and simple here. 
 
There is a fucking possum (OR POSSUMS) stuck in my wood heater in the lounge room. 
 
First, I hear a rustling and look through the glass door and this big furry mass drops down from the chimney and into the heater. Great. Dead possum gonna stink up my hose OR SO I THOUGHT. 
 
I then realize that there is no clear way to the chimney through the top of the heater so now I have 2 problems. 
 
1) Dead possum threatening to stink up the house.
2) How the HELL did it get in there. 
 
I go on cleaning the house, thinking I'll just deal with it later but no, the plot thickens.  
 
The possum is alive. Alive and well. Inside the impenetrable heater. How the hell am I going to deal with this super human possum capable of passing through solid concrete.  
 
I've got a few mates round and I think we are going to make a 'track' to the front door for it to run out of but we have NO IDEA how to make a possum track. 
 
Pics incoming. We're too busy freaking out.   
 
Update: Pics of the beast.