Dguy, aggressive play, by your definition, is is quickly attacking while maintaining a solid defense, and completely keeping the opponent off balance. I guess that's why you would assume that it is better out of the two extremes in styles, but unfortunately I don't think such a thing can really exist. Passive and defensive means that you're not letting the opponent put you in the position that they want you to, and you're creating openings from an opponent currently attacking you.
For one, just because you're passive doesn't mean that they are aggressive. Two, if they are aggressive and you're playing passive, it means that they're trying to keep you on the ropes by your definition, and playing passive/defensive should mean that they're either creating an opportunity through defensive movements or waiting for the safe opportunity to to attack. If you're aggressive, you're more than likely sacrificing defense in some way, because most offensive options can be countered one way or another, with the most extreme case being to stop it before it starts. For example, Fox has a down air to shine that absolutely cannot be punished from anything in or out of shield if done correctly. Fortunately, it won't always be done correctly and after the attack is over, then any number of things can happen, especially if it was only shielded. Fox also has to be in a position where he can do such a thing.
Also, that really just seems to apply to Fox and sometimes Falco. Mewtwo, regardless of knowing the opponent's character inside and out, doesn't have the options, meaning speed, priority, and range to beat down an opponent and keep them off balance. Most of those things seem to come from slip ups of the opponent, poor spacing, and poor defensive and attack choices on their part.
I don't know much about recording and I don't think I'll be going to Florida anytime soon.
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Shellshock: Peach for Mewtwo needs to be a long match for any hope of winning. Basically, Peach is completely covered in approach, has a better projectile, and priority. Some Peach players like Forward air on your shield or spaced to stop approaches, followed with either jabs, grabs, down smash or a retreat.
Call and chase the retreats with grabs at low % and tilts at higher %, and you might be able to forward air out of shield the down smash if it didn't eat under your hard shield. If the forward air hits your shield, you're fine, Peach can't follow up because Mewtwo slides. If it pushes you to the edge, then slowly plan out how you're going to get back on the stage and avoid stupid hits. Basically try not to take unnecessary damage, as everything counts for both people in this match. Peach dies early off of the top except on DL64, and Mewtwo has to die from forward air, neutral air, forward throw and other moves at moderately higher percentages.
If you get Peach off of the stage, and she's at an altitude where you can back air, be patient and wait for a good one to throw and force an air dodge, chase a neutral air and keep chasing until you see she can neutral air you. If she's above you, chase with up air if possible, force Peach to throw her float and double jump cards and keep yourself in a position where you can make something happen.
On the stage, catch projectiles if possible, though her throws are better, if there is a lot of distance, then just back up and baby shadow ball spam hoping for an opening. If Peach wants to be a *****, then you gotta choke her like one. If you're down in percentage, then you gotta turnip/shadow ball approach get grabs/down tilt forward air combos and just slowly rack up the damage for the throw KO. Throw her off the stage and see if you can get some cheap kills with back airs and edge hogs, otherwise take it for the easy % if possible.
A little abstract, but unfortunately, all you can really do is out play the Peach and capitalize on what she gives you.
Hope it helps.
