Well you could have Marth "fall asleep" for his counter and while he's asleep anyone who attacks him gets countered with an attack that gives a lot of damage but instead of making them fly away they fall asleep instead so you land a smash attack.
For the side B you could have him throw his sword like his B attack. Or you could have him use the Flash Step like Bankai Ichigo from SSF2 (
http://mcleodgaming.wikia.com/wiki/Shunpō)
His B attack instead of the throw should have Marth charge up for a flash attack dealing 20% damage. Each charge level should increase the radius of the flash. There should be 15 to 30 charges so it covers the battle field but the side effect is that for each charge you gain 5% damage.
His AAA should have him push the victim forward, teleports behind the person or at least a few feet away from his original spot and swipes the opponent into the air, and teleports again in the air between the distance where he teleported and spikes the person back down a little to the left near where he was in the beginning so Marth can continue the assault/combo.
Or you can have Marth do the Multi-Slash performed by Ichigo from SSF2 (http://mcleodgaming.wikia.com/wiki/Multislash) and if you hold A Marth keeps slashing at the same speed. If an enemy attacks you while slashing or a projectile goes your way you take no hit because you're invincible while slashing and you reflect the projectile back.His side smash up should have him toss a deku nut flash at the opponent with it acting just like the nut; shield-break stuns on ground.
His down smash should have Marth stab into the ground like Ichigo in SSF2 with the same multi-hit and knock back but the entrance graphics appear when he stabs the ground.
His up smash should have Marth jump up REALLY high, as high as halfway up the bridge of eldin 2 V2 (
http://forums.kc-mm.com/Gallery/BrawlView.php?Number=13919&Moderated=All#ByUserID=7470&Moderated=All), raising up the people he catches on the way up with him and when he goes down he thrusts his sword down like Ichigo's down B in SSF2 (
http://mcleodgaming.wikia.com/wiki/Down_Swipe) and spikes the opponents down.
His up B should be the Rising Sword Blade performed by Ichigo from SSF2 (
http://mcleodgaming.wikia.com/wiki/Rising_Sword_Blade)
His up aerial should have him still use the animation of his original up aerial but he twirls his sword like his current up smash.