Q: What IS Scarjumping?
A: It is NOT the repeated walljumping on YS that I am oh, so fond of. It is the very first walljump that I do, which allows me, from the ledge, to walljump slightly below the ledge on the side of the stage WITHOUT using my double jump, that lets me do awesome and relatively easy and effective things such as drop down and scarjump uair > dj uair low recovering Marths.
Q: How do you do it?
A: I let go of the ledge with c-stick backwards, which lets me let go of the ledge with no fastfall or backwards DI, then immediately smash towards the stage on the directional stick. I wait for a very short amount of time, until CF is hugging YS, then smash away from the stage and walljump, never using my DJ.
After that I either aerial after the walljump so that I can control my DI better, or I will immediately DJ back (like I did in IKM), or I will wait a bit and DJ pretty far out, which hopefully unexpectedly lets me reach and kill people who are recovering high.