Heyo!!! Welcome to 20Rx!!!
First off... my advice would be to play whoever you feel the most comfortable with/have fun with the most. If that's Marth than stick with it. Plus, logically, Marth is a better character than Doc so ideally stick with Marth... that said Doc can still give you results but you'll have to put more work.
Coming from a Marth background... Marth's two biggest skills are movement and spacing and Doc needs both of those very much. Just apply your spacing from Marth but adjust it to back air. Doc's movement isn't as smooth as Marth's but it's still pretty good. Unlike Marth, Doc has an easier time killing people. Doc has ways to kill at every percent unlike Marth where 80-150 it's difficult.
Coming from PM Mario background... Think of Doc as a slower nerfed PM Mario. Recovery is worse, combos are worse, more landing lag, but more powerful and a more consistent f-air and up-b. Doc has more tech skill though... for example up-b cancel, up-b extension, aerial interrupt, etc. For me personally, SHBAWD is easier in melee than PM same thing with placebo(waveland after pill). D-air isn't as good as PM although still good if used right. IMO Doc's nair is better. F-air is stronger but shorter range.
I'm sure you already knew some of this but i just wanted to paint a picture of the overall difference... basically Doc is slower but more powerful compared to PM Mario.
Overall just learn the Doc tech...
Things that I would say is mandatory for Doc's to learnl:
- SHBAWD
- Placebo
- up-throw > f-air
- pill game
- perfect wavedash / near perfect
- grab combos
- cape usage
- b-air spacing
- d-air auto cancel
- wavedash back in neutral to counter approach (this is huge)
- up-b cancel (not huge but it's really good against shield pressure)
I would say starting learning this things in addition to Doc's neutral...
Speaking of neutral... compared to the other two characters you used to play (Marth and PM Mario)... the biggest difference is that you will be in neutral a lot more. One of Doc's biggest weaknesses is his combo game powerful but short. In other words you will have to accept that you cannot 0-death fast fallers in the way that Shiek or Marth can (final destination being the exception). You also have to accept that as Doc, you will have to give up on the initiative. You cannot approach in the way that Sheik or Fox can. I'm not saying you can't approach... but it's not the same as the previous two characters you played. I would say that it's better to get your opponent to make a mistake and punish then it is to approach. Either wait for an opening or make one but you can't brute force one. You can't rush in like Falco or Captain Falcon. That is something that you will have to accept. An example, as I mentioned in the above list, wavedash back on Doc is incredibly good... just dash dance and when you see an approach wavedash back and punish.
In regards to actually playing Doc... check out the stickied posts
here's a
post from me explaining some stuff to another new Doc player
check out the tech skill thread if you want to learn some new stuff
and most importantly if you do decide on this character:
Have fun with the good doctor!
