Interesting question. Here are the revised sentences, complete with commas (when they are needed).
After I finished the Chicago Marathon, my legs were tired.
Muhammed Ali was the greatest athlete ever.
My mom told me to clean my room, wash the dishes, and take out the garbage.
I want to listen to my iPod in class, but my teacher won't let me.
If I had the chance, I would change our mascot to a gorilla.
No, I don't want to go to Taco Bell for lunch.
The fireworks were fun to watch.
Marcus Brutus, who was tricked by Cassius, was the last conspirator to stab Caesar.
Antony, thinking the conspirators would kill him, fled after he saw Caesar's dead body.