On the topic of using the C-Stick, I currently use the C-Stick set to Smash, but I am gradually making the switch to C-Stick Attack.
My main worry was that it's a lot easier and quicker to space a tipper Fsmash with the C-Stick, and this was why I was unsure about making the switch. However, I recently found out the joy of the A+B Smash function. With this, I can still do my walking Fsmashes (when needed) with ease, and I can still use the C-Stick to tilt. Another example is me miss spacing a tipper with not using the C-Stick. Of course it is well known, but landing Uair into tipper Fsmash is very nice, and I go for this option quite a bit. Having the C-Stick makes landing that tipper that bit easier, but without it, I used to occasionally move forward a bit first, missing the tipper and getting the sourspot. However, with the A+B Smash option, I can do much the same thing as with just the C-Stick, and it's just as reliable.
Like I say, still making the adjustment so far. I'm not confident/competent enough yet to use it in a tournament setting (like I went to a tournament on Saturday, but I still used C-Stick Smash as I am not confident enough yet. Also managed to get 5th, yay), but I am seeing a lot more positives to the tilt stick.
Just for clarity, this is my control setup I am leaning towards now for Marth on my GC contoller (anything not mentioned is set to default):
Rumble - Off
Tap Jump - Off
A+B Smash - On
C-Stick - Attack
For certain characters, I have the L button set to Jump (Rosalina for example), as I find it a LOT easier to follow up in the air using the L button and the C-Stick to Up Air etc. However, with Marth, I find SHAD a lot more benefitial, and I find it a lot easier to use the L button to air dodge rather than R. As I use Y for most jumps/short hops, I find using the same hand to do the jump and air dodge makes me mess up one input (either I FHAD, or I short hop and don't air dodge), so using different hands for the two inputs I feel is a lot more reliable. If I can somehow master being able to quickly short hop and air dodge with Y and R, I will universally switch my L button to Jump.
One final question regarding the C-Stick topic; Does having the C-Stick set to Attack stop you from fast falling a Dair? I can't say I've took much notice to whether it does or not.
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Thanks to Fair's power and range I was able carry a Villager off-stage and kill with short hop Fair > double jump Fair > tipper Fair. It killed from around 70 iirc with minimal rage.
Don't know whether this was possible before the patch, but the other day I got a pretty sweet combo/string on a Mega Man. It consisted of short hop sourspot Fair, sourspot Uair into fast fall, full hop Fair, tipper Fair. He was at about 50% when this worked, and it appeared that he couldn't get out of it. Though it didn't kill straight away, it set up nicely for an edgeguard which I quickly took advantage off and finished the stock.