So my coolant has been slowly disappearing over the past few months. I've had to add coolant about every two weeks, but it has gotten worse the past week or so. It has also started to run rough for the first minute or so of running. I have been checking the oil and have not seen any sign of coolant. Today I pulled the plugs and most of them look like this: BUT, the rear passenger plug looks like this: Any suggestions as to what this is? I think a bad headgasket.......but its not mixing coolant with the oil yet.....

Your head gasket is most likely on it's way out. It's probably just leaking around that one cylinder and it's probably small enough that most if not all of the coolant is getting burned. Is this on your 2.8 or 383?

It is on the 2.8 V6.......but its my daily driver

Is there an easy way to check to verify its the headgasket?

Could it possibly be bad rings or valve stem seals?

The plug does look kind of oily so it could be oil, but that really wouldn't explain running rough. Take it to a respectable mechanic, throw some money at him. And he'll do a head gasket test. If your headgasket is good than you might look at your radiator for the disappearing coolant. Don't know what year your car is but it's at least 19 years old and if your rad is original it may very well have some small holes. My bird does, not worth fixing at the moment, but they're there. I'm not very knowledgeable on 60* motors (although I better start learning). So I can't really help you much from here, sorry.
Alex

Seriously? You want him to throw some money at a mechanic to look at it?
If you have already thoroughly checked for leaks everywhere (and with that plug like that.)
Pull the heads, check the gaskets and check the heads with a straightedge. At worst if you have to have this car to drive know where to have a good set of heads on stand-by in case you find something wrong.
One time I had a Ford head that cracked under the exhaust manifold where I couldn't see it and by the time it got hot enough to leak it burned off before it would drip or show itself.

Well, ya. He asked for the easiest, quickest way. Pulling the heads is not the quickest, and for most not a very easy, thing to do. Although it is the better choice. If he takes it somewhere he should know in a day and he really shouldn't pay more than $80.

BTW, how many miles are on the car? If it's more than 150k your heads are most likely on there way out. And a new set of heads would be a good idea.
Alex

Do a compression check. There are shops that can also do a test for combustion gases in the cooling system.

Could be a cracked head.

Go to your local Midas. They do a free compression check and look for gas fumes in the coolant. It takes like 2 mins to check but they have to wait for the engine to cool down so they can take off the radiator cap.

IT's quick, easy and cheap.