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I would learn as much as you can about the Fegatello (Fried Liver) Attack, used in game 3. It's not hard to memorize because a lot of the moves are forced and actually make sense, and you'll win a lot of games with it if you know it fairly well, because of numerous opportunites for your opponents to blunder as they did here with 7...Ke8?
Black should look at the Ulvestadt, 5. ... b5!? as an alternative to the bad 5. ... Nxd5 or the well-analyzed 5. ... Na5. Of course, there is also the Wilkes Barre, 4. ... Bc5, but even I'm not crazy enough for that line.
5...Nd5 isn't that bad. I like the Fritz Var 5...Nd4 which often transposes into the Ulvestadt Var (5...b5), which can also transpose into the Fritz Var...