So in general, Lucina and Marth destroy Ganon but he does have a few things that you should watch out for so I’ll start with those.
First, Ganon’s moves do a lot more damage and knockback. This means that Marcina will have to make more neutral reads than Ganon will, especially if he gets a good smash attack read.
Second, you have to be wary of Ganon’s burst options. Marcina likes to space out of the opponent’s range and poke at them so sometimes Marcina can be caught off guard if their opponent has decent burst options that can invade their space. The good news is that Ganon’s burst options are fairly slow and very punishable if whiffed, so as long as you respect those options they shouldn’t be too hard to deal with. Specifically, you want to spot-dodge Side special (you can beat it out with your moves very comfortably but that takes better timing) and you want to shield Dspecial. You can also dash back and punish the endlag of both moves but that takes a really good read to pull off.
Third, Marcina cannot compete directly with Ganon’s smash attacks. A lot of times Marcina can out range and box out characters but Ganon’s smashes are just too big. You especially want to avoid landing directly on top of Ganon or on a platform above Ganon since his Fsmash and Usmash will destroy you. He also gets a lot of mileage off of dash back Fsmash (or Ftilt) to counter approaches. Dsmash covers opponents that try to roll behind Ganon so don’t get predictable with rolls. Also, don’t let him ledge trap you with his smashes. If you use a ledge option too quickly you’ll get hit by them.
Those are the main things to watch out for now let’s go over Marcina’s advantages.
First, Ganon has a VERY hard time landing against Marcina. His Dair loses to both Uair and Utilt and he’s slow in the air so he has a hard time drifting away. He can use Dspecial as a mix-up but it has a whopping 42 frames of landing lag, so he’s EXTREMELY punishable if he doesn’t hit his opponent. For the most part, especially on platform courses, you want to shark him with Utilt not Uair. If you go for Uair too often he can react with an airdodge and make you whiff, ending the juggle. Stay grounded for the most part and shield if you see him use Dspecial. I’m not saying that you should never use Uair, you should always mix-up what you do to keep your opponent guessing, but it shouldn’t be your primary option. You can also empty short hop and fast fall to bait out an option. When he sees you jumping he’ll assume that you’ll try to Uair him and react with a panic option (either airdodge or Dspecial) which you can read and cover. Everytime he’s above you, you should be getting a few extra hits before he lands.
Second, Marcina has more range and mobility than Ganon. Now Ganon has quite a few moves with a lot of range so you should respect his range, but in general most of your hitboxes will beat his. Your moves are also disjointed, whereas his generally aren’t. There are quite a few times when I fought Ganons where we both used Ftilt, but because he sticks his foot out my move connected and his didn’t. Ftilt, Nair, Fair and Dtilt are great options to keep Ganon at bay (if they’re well-spaced). Fair covers the area immediately in front of Marcina and a lot of characters have a pretty hard time contesting it. Most of the time, falling short hop Fair is better than rising SH Fair since it has a lot of recovery time and at max range, its low landing lag makes it hard to punish. However, rising Fair is good at stuffing approaches, jumping and rising aerials. It’s just that Fair takes a long time to recover in the air and doesn’t last long so it can be punishable. Nair is good as a falling aerial and as a rising one. It's only -4 on shield so only the quickest out of shield options can punish it and Ganon doesn’t have any. Retreating rising Nair is also great for walling out opponents. Against the slower characters, especially Ganon, I like to dash at them buffer a SH Nair and drift back. Lucina has poor airspeed but she has great air acceleration, and most importantly, she gets more acceleration from the control stick. This means she can control where she goes (as opposed to Roy/Chrom who have good airspeed but mediocre air acceleration and can't change direction much) and that's important for spacing out your aerials. Ftilt is good out of a dash and for walling out opponents if you're standing. I find it especially useful for stuffing opponents like Jiggs or Yoshi who jump in and can't contest Ftilts size. In general, you have to be patient to win against Ganon. You should use your hitboxes and speed to control neutral and deny him space instead of trying to rush at him recklessly and swing your sword at him. Keeping center stage is very important for Marcina since it limits what he can do in neutral.
Third, you should destroy him offstage and at the ledge. Ganon is pretty slow in the air, his recovery is not that great and he has mediocre options off the ledge. Here is a great video by Zero explaining ledge trapping to help you get started
https://youtu.be/2EdcYPajncg I don’t know of any videos explaining edgeguarding with Marcina specifically, but if you watch MKLeo or Mr. E you can get a good idea about how to edgeguard. If I find one a good video explaining edgeguarding, I’ll post the link here for you.
Fourth, Marcina’s out of shield (or OOS) options really throw off Ganon’s gameplan and you should abuse the heck out of them. Specifically, you should focus on using Uspecial, Fair, Bair and Nair. You should avoid dropping shield and punishing with your ‘A button’ moves since dropping shield alone takes 11 frames. So dropping shied and using Jab takes 16 frames and dropping shield and using Fsmash takes a whopping 21 frames. You should only do this if you’re punishing something REALLY laggy like Ganon’s Dspecial (which is -29). Uspecial is the crown jewel of Marcina’s OOS game. It comes out on frame 5 and beats every move Ganon has, with the exception of his Bair which is -4. Now you shouldn’t get TOO predictable because there is counterplay to Uspecial OOS. If Ganon spaces his moves outside of Uspecial’s range or if he empty-hops to bait out your Uspecial, then he can get his shield up before your move and you’ll whiff if you go for it. If he crosses you up, you’ll also have to recognize that and reverse your Uspecial otherwise you’ll be wide open for a big punish. Nair, Fair and Bair OOS should be used primarily to punish his tilts and smashes (except for a well-spaced Fsmash which you should avoid trying to punish entirely). Nair and Fair come out on frame 9 OOS and Bair comes out on frame 10. Most of his aerials (as in all of them except Dair) are -8 or better on shield so you should only punish falling aerials with Uspecial. His Tilts are all between -12 and -17 on shield so Marcina’s OOS aerials are the optimal punish. Rising Fair and Bair OOS also set up tech chases that can lead to jab reset combos for easy damage. Ganon’s jab and dash attack are -8 and -9 on shield respectively so you should stick to Uspecial to punish those.
https://ultimateframedata.com This site has frame data for every character along with shield disadvantage info. You should use it a lot!
Finally, Ganon doesn’t have great OOS options himself so you can get away with a lot of shield pressure. His fastest OOS option is Nair at frame 10 and his shield grab is frame 12. Lucina specifically, can generate a lot of shield pressure with her aerials. Nair is -4, Fair is -6, Bair is -5, Uair is -3 and even Dair is only -9. You should watch videos of Mr. E for ideas. He uses Lucina’s shield pressure very creatively.
Well that’s all I got. Sorry this was so long, I wanted to be as thorough as I could.
