Marth is a very balanced character, who has speed, range and power all packed together to create one of the games most capable opponents. Marth isn't all advantages however and does have some significant weakness that can be exploited fairly easily with a bit of effort. First of all Marth is extremely light for a guy of his size, lighter than Pit in fact which means that you shouldn't have much trouble KOing him. Comparatively Marth doesn't have much trouble KOing you either as his smashes are strong and will KO you at lower percentages, especially if Marth manages to land a tipper with any of them. However none of Marths smash attacks are safe for him on block but i'll delve into that a bit later in the summary.
Another weakness of Marth lies in his recovery. Marth has good vertical recovery with his Dolphin Slash (Up B), however his horizontal recovery is extremely poor and generally if Marth is sent far enough from the stage it becomes pratically impossible for him to recover. This is one aspect of the matchup where a Pit should definitely aim to take advantage of. Pit's Arrows eat away at his jumps and push Marth further away from the stage, coupled with the fact that Pit can WOP Marth off the stage as well as reverse the direction of his Dolphin Slash with his Mirror Shield all make for quite an advantageous situation once Pit gets Marth offstage. Pits should however still be wary when chasing a Marth offstage with a WOP as Marth has more than enough aerial options to challenge Pit even when on the defensive, therefore your best option is to generally ping Marth with Arrows to eliminate his second jump before attempting to WOP him, therefore even if he attempts to try to prevent your WOP by attacking you he still remains in a disadvantageous position when trying to get back to the stage. If you're feeling confident you can even attempt Mirror Shielding his attacks offstage as a sort of psuedo-WOP, but it is discouraged as you generally have safer options.
Marths last real "weakness" is that most of his attacks including all of his smashes aren't really safe on block unless spaced correctly. This "weakness" isn't as easily exploited as his other ones especially with Pit's comparatively poor melee options in this matchup but it is possible to create openings in Marths game with which you can capatalize on, primarily your grabs which can lead to other follow-ups and your Fsmash which can punish Marth relatively well OoS. You don't really have to worry much about diminishing your Fmash in this matchup as your Dsmash will generally kill Marth around the same percentage Fsmash would and for the most part just as reliable. You can however alternate which move you want to use, Fsmash as the punisher and Dsmash as the killer or vice versa, but take care not to readily use both moves for punishing least you diminsh both to the point where they are hard to kill with. In addition Pit will always force Marth to approach due to his Arrows which means Marth has to take the offensive in this matchup. It's at this point when Marth has gotten inside his comfort zone that you now have to focus mostly on your spacing. For the most part in this matchup you are going to want to get underneath Marth where he has somewhat of a blindspot. Your Uair, Dthrow, Usmash and Utilt are great moves when in this position and will help greatly in building up damage for a possible KO. However take care not to be too predictable as Marth's Counter (Down B) can seriously put a damper in your plans if you give him ample oppurtunities to use it.
