Actually Marth don't need an agressive style, I think.
He needs a defensive close-quarters style.
Marth needs to be in a reasonable distance from Snake (that distance isn't too much), and attack in the exact point, waiting for his delays and such. He can't hesitate, but needs to have caution. But this is more when he is on the ground (stupid tilts lol). In the air he is a naked snake.
Imo Marth needs to 'feel' the exact momment to attack.
For the granades, you can't really catch them if your opponent is a bit smart.
He won't give you time to counter-attack the granade.
Just avoid them or catch and instantely Air Dodge.
And don't try to catch with an aerial for obvious dumb reasons.
I can be very wrong, like I said, I still want more experience.
Please don't let this stop, discussing match-ups is so fun
XD~