Well...you gota first work on yah speed. Marth can move faster then that. I saw some dash dancing, which was good, but some of your follow ups were not that effective, but fear not...everything takes practice. Trying doing spaced SHFFL Fairs/double fairs out of a dash dance, along with grabs and dancing blade, or even a wavedash back. Mix it up a bit. To do a space fair, just jump, forward A, DI with your analog stick, flick he C-Stick Forward and then l cancel. That should prevent you from getting shield grabbed.
Your lag canceling needs a bit of work. Both you and your opponent missed some which made you both a bit slower then usual. Now as for edge guarding Ganon with Marth, just use your down tilt before he can touch the stage. A tipper hit should be enough to clam his stock. Or, you can stand near the edge of the stage, wavedash off the stage and bair him, or grab the edge, jump away and bair him that way. And as mentioned above, keep Ganon in the air with your uptilts. I noticed you messed up a bit and did Up smash instead, but that is a common Marth habit that will indeed pass over time. So yeah, you and your opponent should spend alone time in training mode and practice your cancels more. I find it better to train alone in training mode instead of practicing the cancels in battle. That Ganon was not too serious in the combo area. If he canceled right your Marth would have most likely eaten a down smash to a fair or some other aerial from Ganon.
So yeah, you have an idea to some degree what to do. Just gota keep at it. Good luck.
