Both will play the same poking game and will have about the same level of safety overall, none really *need* to commit and both keep opponents away from their zones very well.
But the Knockback values on some of Marth's moves (mainly Dancing Blade, Fair, Bair and Ftilt [particularly Ftilt]) will make a huge difference, because he can "accidentally" kill opponents without really fishing for anything else other than his regular defensive and punish game. Lucina doesn't have this luxury and will have to either prolong her neutral exchanges for much, much longer than Marth's average interactions (and that is very important in high-top level play, where you'll be facing Top Tiers with similar or better neutrals that will keep on contesting or outright beating yours) or burst out of her comfort area and commit into a more unsafe option to score a kill.
Bolded is a topic that I've been mulling over for a while. "Accidental" kills are the kind of thing that can catapult characters up tier lists, and it's instructive to think about which Smash 4 characters this applies to. Obviously, when you get your opponent to high percent, you start looking for an opportunity to land the KO strike, whether through strings, confirms, edge guards, or whatever else. Characters that are "good at killing" make it more dangerous to be at high percents against them, but they often do so in different ways.
The simplest kill option for most characters is the Smash attack, but nearly all of them are punishable on block, to say nothing of whiffs. You'd like to be able to throw out Smash attacks in the neutral, but that's gonna get you kicked in the teeth (for most characters, I'll talk more about the most obvious exception in a moment). If you have to rely on stray Smash attacks to take stocks, your character is not good at killing. So what's next?
50/50s, traps, and kill confirms off of low commitment moves are more reliable than Smashes. Grab confirms are strong for beating shield, but it's worth mentioning that most grabs have a punishable amount of cooldown. Kill throws are similar, often requiring a committal grab and/or high percent on the opponent. Furthermore, your opponent must be within certain percent ranges, or at a certain position on the stage, or be hit with exactly the right hitbox of the setup move, or perhaps a combination of all three. This can be a particular problem if the second half of the kill is very committal, like a Smash attack. If you are just a hair too slow, or you miss your setup slightly, you have to be aware of it, lest you miss the follow-up and eat a punish. The best confirms in the game have lenient windows to execute and do not require finicky hitboxes. (Diddy's D-tilt is a good example. The tilt is fast, non-committal, and confirms into multiple moves. Note that U-Smash does not always connect fully, though, and often U-tilt is the safest option, killing much later.) Reliable, lenient kill confirms are common across the top tier. I perceive Fox as kind of an oddball here, in that a lot of his confirms/traps have tight windows requiring precise hitboxes, but he has a bunch of them, and his moves are universally quick enough that you can never be totally ready for which one he'll try to hit you with.
The third way to be good at killing is through stray hits off of safe moves, and I think this is the rarest variety of dangerous character: the "accidental" killer. To be in this category, a character has to have a fast, low cooldown, versatile, safe move that's a good option in neutral but also starts killing at early percents, relatively speaking. Furthermore, that move can't be the character's only powerful neutral option, or else the opponent will always be on the lookout for it. The simplicity of the accidental kill move is what makes it dangerous: there are no execution concerns, no worries about following DI, and no finicky conditions or windows. Essentially, you skip the advantage/punish state. You play the neutral as normal, and then, on occasion: "Oh, look, I killed them. How about that?" Especially over a long tournament in a high-stress environment, that ease of use is enormous. I said that I think that few characters have this luxury, so let's make a list:
- Mario's U-Smash: The biggest exception to the "can't throw out Smashes" rule. Fast, safe, and very dangerous.
- Marth's tipper F-tilt and aerials: The aerials don't kill obscenely early, but the F-tilt does. A fast, long range move that can start killing alarmingly early, especially near the edge. F-tilt is also notable for being a low-commitment second half of another Marth kill setup, in which it follows from jab. Absurd button.
- Corrin's Lance: Fast, safe, and long-ranged. I think it's harder to kill people out of the blue with because of how much Corrin uses it, and thus how expected it is, but it still catches opponents frequently.
- Robin's Levin aerials: a bit wonky, since they're not always available, so they're not the sort of always-looming threat as others on this list, but they hit like a truck. Not incredible in the speed department.
- Funnily enough, Ganon's U-air, N-air, and B-air: All of Ganon's kills are going to be random kills, but his aerials are actually really good, in terms of range, speed, and kill power. This example is particularly noteworthy, since even the rare trait of "accidental" neutral kills doesn't guarantee a good character.
- Mewtwo's F-air: The one i'm most familiar with. Frame 6, good combo move at early percents, starts killing early, does 13% (God only knows why). Nonsense move.
- Mac's F-tilt: Frame 4, first hit tramples, insane option. Primarily works on the ground, but that's where Mac wants to be anyway.
- Luma: Gets very silly with rage, turns normal moves into must-dodge monsters. Luma is a collection of random kills, but you can also get rid of it, which has started to hurt Rosalina at top level.
- Cloud's U-air: Often stales, and it was nerfed, but still monstrous, particularly for how hard it is to even trade with.
- A lot of Lucario's moves, once he has enough aura, but he doesn't have a lot of incredibly fast options.
I'd like to see what other moves the thread thinks qualify for this status. From the above list, the really threatening characters are Cloud, Rosalina, Mario, Marth, and Mewtwo, all of whom have strong, varied neutrals to surround their random kill move, making it even harder to avoid, and their moves are all quite fast. Maybe Bayo's B-air belongs here, or DK's, but they don't kill super early, to my knowledge. Maybe I'm remembering wrongly. Sheik is antithesis of this kind of character. She has a variety of ways to kill, but she almost never gets "random" KOs, which is part of why she's not as common at lower levels of play. Even her Smash attacks aren't that strong, tipper U-smash aside, so she has no beginner-friendly way to kill.
From a game design perspective, I'd also like to hear what we think of these moves. Do we like them? Do we hate them? Would we be okay with buffing a lower-tier character's move into one of these options? That's basically what happened with Marth and Mewtwo (Mewtwo's F-air was already good, but made better with a bigger hitbox). Would these options be more acceptable without Rage in the equation? I kinda get the sense that these options are unpopular. We've heard a lot of griping about Mario's U-Smash being dumb. Nobody likes Luma. And when the devs want to make a character better at killing, they often go for grab confirms, which I find sensible. It's a very fine line to walk when giving a character "accidental" kill moves -- they can get very stupid very quickly. I love Mewtwo's F-air, but it's a silly move (13%!). Should killing be hard and/or risky for everyone, or is it okay for some characters to have supercharged kill buttons?
