The first thing to do is to check the oil level to see if it is over full. Sounds like the carb float vavle may be sticking and you might be getting gas in the oil.
Bad piston rings, oil level is too high, check the oil level and adjust
The smoke from your muffler has a smell because what is coming out of the muffler is the products of the incomplete combustion of your fuel. Some of those products are gases and vapors that have color and some are dark but small particles - that is what you call smoke. But some of what comes out are various chemicals that your nose detects as odors.
Many times it just means that the mower has been leaned over on it's side too far and oil has gotten into the breather. It will burn this off after a while. If it persists then you have an internal problem in the engine and are getting alot of blowby into the breather.
Some engine oil has entered the muffler when the mower was tipped, it will burn off after you run it, make sure the oil level is correct (don't overfill) as this can cause similar problems.
Just having a hole in the muffler won't cause smoke to form. Any smoke coming from an engine is caused by either environment changes (white smoke while engine is warming up), or an engine burning oil (blue smoke). Sometimes even a bad catalytic converter can cause smoke. The hole in the muffler simply gives the smoke a way out. Trying looking for external oil leaks or checking he oil level occasionally to see if it is burning oil. You may see water vapor is there is a hole in the muffler but it wouldn't last long once the muffler warms up and the moisture is burned off. She shouldn't see actual smoke unless there is a problem with the engine.
No this is not normal. Depending on the color of the smoke, the engine is either burning oil, or the fuel/air mixture is off and the fuel is not burning fully.
You may have a blown head gasket.
It is need of a service.
One reason that a lawn mower may begin to smoke is that the oil chamber is too full. Spark plugs that have burnt oil and are not cleaned can create smoke and other exhaust issues.
The most common reason for your Pontiac to lose oil and ex smoke from the muffler is a broken piston ring. A malfunctioning exhaust valve can also cause the problem.
The car might not start. If it does start, the banana might shoot out the tailpipe. If it is up in the muffler, it might smoke or burn.
It sounds like you are burning oil. Is it dense, or just a thin cloud. Check your oil level, if it is too high, you can force oil around rings and burn it. The rings on the pistons could also be shot. What year/model/etc. is it? Also, be sure to check your oil every time before mowing, and after for that matter. This will prevent overheating, and also a premature rebuild.