Borodino, scorched earth tactics, and Winter pretty much.
Borodino makes for a very interesting topic. No signs of the tactical brilliance or killer instinct (think "One sharp blow and the war is over" at Austerlitz) that had defined Napoleon's decisive victories in past major engagements, just a simple all out attack against strong positions relying on simple brute force. A potentially decisive opportunity finally presented itself at the end of the day, the French offensive finally opening up a large hole in the Russian line (both armies now totally exhausted with the French Guard regiments the only force left capable of carrying out an attack with any vigor). Still Napoleon refused to grasp it, waving away numerous officers (and finally Ney) as they urged him to commit the guard and smash the Russian army in detail. Instead the Russians are able to hold out and withdraw in good order at nightfall.
Edit: Come to think of it, from the tactics down to Napoleon reportedly being ill there are quite a few similarities between Borodino and Waterloo.
Then of course there's Napoleon's second major (and extremely costly) mistake; waiting a month in Moscow for a surrender that wasn't coming. The only thing that could have saved his army post-Borodino would have been withdrawing to Poland upon finding Moscow a scorched ruin. The pause there was absolutely fatal.
Also if your school has access to academic websites, academic sources are always preferable. Google Scholar is a really good resource too.
