Great games Kar!
I'd say stick with the normal Ganon side-B, personally. I'm not a fan of the that custom, as it takes away a little bit of the mix-up game Ganon has. Not to mention his normal grab is garbage, so he doesn't have much of an answer to shields with out it.
The custom down-b is great, though it is much more punishable than you'd think by watching me eat it each and every time. I think part of the problem is that for the most part, you were following it up with the forward tilt or down tilt. I think that's a great combo to use, but maybe a little bit less often.
I liked that you started to use Ganon's neutral air, which usually is not seen too often. It was blocking my air dodge, as you obviously noticed, so great use of that.
Personally, I think you were doing better in the matches where you relied on the B-moves less often, and stuck with spacing out Ganon's normals.
All in all, good stuff! You'll be a force to be reckoned with in the Ranbats for sure.
Thanks for playing!
Edit: In regards to down-air, I was actively trying to avoid it-- so what I was doing was changing the timing of my up-b. To counter that, your best bet would be to down-air a bit earlier than you normally would (or later if I waited, but that was rare). Easier said than done, of course. It's all about prediction at the end of the day.