The only sin i can possibly commit is using projectiles extensively if a opponent keeps distance. Some will say that’s how you play but i keep seeing people who complain about projectiles so I guess it’s a sin.
I don't really mind projectiles if they're being used as a combo starter or as a tool to approach, but when your opponent uses it as a tool to camp you because they know they can't beat you head on, that's what really frustrates me and is one of the few situations in which I'll teabag someone. I mean, I get it, sometimes you have to camp, especially if you're at a high percentage, going balls deep against someone face to face just isn't smart. The thing is, though, online it seems that's all people do. Samus, Richter, link, young link, palutena, etc. Run to the side of the stage and spam projectiles. I main jigglypuff, so it's especially frustrating because I have no projectiles of my own or something like a ridiculously long sword to get you with, I have to masterfully bob and weave through the BS, predict where you may flee to, and get the punish.
I know complaining about it can be seen as kind of a scrubby thing to do, it just seems unfair that stopping/punishing projectile camping for a lot of characters involves a degree of skill, patience, timing, etc. and a lot of risk if you screw up (Whoops, miss timed the air dodge, guess I'll take this massive energy ball to the face) whereas projectile camping doesn't involve a whole lot of thought and is a relatively safe option against quite a few characters.
As for my own "sin" I played a team battle against a Samus and Mewtwo today, and its rare that I get teammates that know how to properly synergize with puff. I was paired with Chrom, and inevitably, guess what both of them wanted to do? Play keep away and spam projectiles! This is at around 3.5 million GSP I think? So, right around "elite" skill levels. Lol. Anyways, my slow fall speed and well, slowness in general makes it difficult for me to get back down and support my teammate when I get knocked back. Smart teammates realize that and try and get back to me instead, but this Chrom decided to try and rambo both of them by himself and ended up leaving me by myself, at 80 something percent to kill a two stock Samus at mid percent and a single stock mewtwo at midpercent.
So, Samus decides to teabag me, which triggers me juuuuuuust a little bit. I killed mewtwo by gimping his recovery, and put the beatdown on Samus. It was Luigi's mansion, all I really had to do was alternate between pound and short shop neutral air on the bottom floor and he got smacked around for days until he lost his stock. But I was at 123% when I took it. So I waited out the m'fing timer for three whole minutes for the sudden death match. He couldn't catch me, it went to sudden death, and I killed him with rollout, lmao. Normally, I consider this a mortal sin and I'd throw something, but if you play like a coward and teabag, nothing is better than a taste of your medicine.