well, you don't really want to approach marth. you want marth to come to you. that's why falco has a gun and without that gun the match would already have been won by marth. camp lasers. there's no such thing as too much lasers. if your friend *****es, tell him to deal with it. pick a corner and shoot lots of lasers. when he approaches to you, jump away or quickly attack then run away and shoot more lasers. basically you want to piss marth off. when he misses something or makes a dumb mistake, that's when you want to approach, when he's off gaurd. catching him off gaurd is the safest approach. cause if he's just camping in his sheild and you try to SHL SHL dair shine, you'll get grabbed or something, then he'll chaingrab you and utilts and all that dumb crap. i also enjoy using a lot of grabs against marth. all the throw directions work and you don't really want to spam one cuase then they'll predict it and retaliate. you can techchase on dthrows and grab again, fthrow and nair or something. throws are too good on marth. also, learn to DI his tippers. you really shouldn't die from a tipper below 80% near the edge, or below 100% if its in the middle of the stage if you DI well (on stages with larger kill zones of course, you'll pretty much die grom any tipper above 60 on yoshis story) to DI, hold the cstick towards the stage and hold your control stick up/towards the stage diagonally before you're sent flying. (usually before the hit if you know it's going to happen)
