Neutral

At this range Marth can react to falco's aerial approach with a dash back pivot grab.

In the same range though if falco expects you to dash back he can come forward with a laser beating your reaction dash back.

To beat falco's approaching laser what marth can do is a nair in place instead of dash back to intercept falco.

Marth can also use jab to prevent falco from running him down. Which when tipped sets up the range you want to be at. This can also beat aerials if done right timing or distance.

At this range marth can dash forward nair drift back proactively to cover multiple options from falco, it's very effective. This beats approaching aerial or laser as well as aerial in place or laser in place.

One of the most common options for falco to punish marth's nair is to move away then punish the nair landing. Marth can beat this by dashing forward and jumping forward then mid height to late fair on reaction to what falco does.

Marth can also use dash in side b to catch laser in place at about this distance. It can lead into a grab if done right.

Sometimes when cornered falco will full hop to get away from marth when he moves forward or will do full hop on reaction to marth coming forward. So if marth does the jump drift in again he can fair falco as he jumps to full hop.