This tech isn't unique to Doc, but his applications of it are probably among the most interesting.
On stages with walls (not including Omega Pac-Land where you can't walljump but including FD), you can buffer a walljump from the ledge by quickly doing a Dashdance motion after grabbing the ledge.
This is a way to ledgehop B-air without using your 2nd jump (though it doesn't send you very far into the stage). However in terms of edgeguard options, this is where things get really cool.
You can for instance do walljump U-air/Cape and regrab the ledge.
Walljump D-air allows you to deny ledge sweetspots or people hugging the stage pretty consistently if set up correctly.
I suggest people try it out.
Another thing is Fullhop Pill is glitchy. Apparently if I'm seeing things right, it puts you in a state where you are effectively 1 frame from touching the ground while your Special Animation is ending. Now if that sounds confusing, just remember that 1 frame state transitions are the reason why we had glitches like ISJR in Brawl.
Why does this matter for Doc? Because buffering any aerial during this window will put you in your landing lag animation, even for ones that normally autocancel before the hitbox is active. Most IMPORTANTLY, this applies to D-air, which has a landing hitbox, so it's technically an option after fullhop Pill to defend yourself if people are trying to catch your landing.