Against Marth, spot dodge your ass off because if they are aggressive instead of campy, their spacing is going to be god awful meaning you'll get a free grab. Dont try to have an air battle against Marths because you'll lose 100% of the time. I tend to do this 100% of the time because Im bad at taking my own advice. As for recovery, if you get blasted Yonderweiss, then PTP first. The key to Doc's recovery is to not use your jump immediately, if you do youre as good as fucked. You wanna use your jump when youre closer to the stage so you get as much horizontal push as possible. But yeah, I dont play Doc much anymore, half the stuff I say is nonsense but take it to heart if you choose to :D
Forgot to mention Doc's weird UpB sweetspotting shit but I cant really explain it so Ill have to show you or you can go look it up. Its good to know.