Falchion refinery for Marth?

He makes a great buff-bot with the special refine and and hones or spurs in C and S, otherwise +Spd is always going to help him survive and kill.

You might want to try a "drive" skill in C slot and the Drive Def seal.

Combined with his refined Falchion he does a nice job buffing.

your marth is +atk - res, you can do 2 things with the falchion:
1- Make him support using the refine to add +2 all stats for all allies in 2 spaces, put drive res, def, atk or res in skill C and drive def on S, or;
2- Increases the atk using refine and put seal def (skill b) to increase even more the atk.

Trust me on this, the buff falchion is one of the best weapons in the game, not upgrading to it wastes so much potential, everyone around him instantly gets stupid buffs, and you can still use him as a decent Dragon killer.

Trust me on this, the buff falchion is one of the best weapons in the game, not upgrading to it wastes so much potential, everyone around him instantly gets stupid buffs, and you can still use him as a decent Dragon killer.

IMO, if you are going to refine a legendary weapon it has to be the effect, because I just don't think it's worth spending 200 Divine Dew for a little boost in stats, even though it's tempting. If you want HIM to fight better, give him a wo dao+ or slaying edge+ and refine it of course, it's just 50 refining stones, but if you want an amazing support unit, refine his Falchion's effect, give him drive def sacred seal and another drive skill or spur in his C slot, you can even give him reciprocal aid so he can heal. I use him with my LA! Hector (they have ally support) and Hector tanks almost anything with that support and then Marth can heal him

Those are very solid offensive stats though the speed refine would serve him very well.
If you don't want his drive support I would heavily recommend that.