Too many. I'm that kind of person. Heh.
First and foremost is the direction I went with my first few uploads. Pigeonholed myself into a fetish niche. I can't help but be thankful to the communities that love me but, I never wanted to be a "CattyN" y'know? I envy those animation channels doing stuff like pop culture parodies. I get really burned out on all the wedgie, spanking, and inflation requests in my comments. Maybe I'm looking at it wrong though, maybe this is the most unique path to a big transition.
Not doing music alongside my cartoons early on. It came out of "nowhere" this year and I can see why people didn't listen to it. In my defense I have much better equipment now and have improved so much as a singer since 2010 so maybe it's okay I didn't do it then.
Skipping 2006. My first animations were actually finished between 2006-2007. I was way too scared to share them with anyone but friends and family. Maybe I'd have a much bigger channel now if I had uploaded them as that's when YouTube was literally brand new (not that those animations were anywhere near what I'm doing now).
Fullscreen was a four year mistake. They were also brand new when I joined so MCNs weren't such a controversial thing yet. Not a ton of regrets though, it gave me a 'show' and I did a lot with the partner customization.
Giving into fear and doubt. All those little "what if" moments where back then I was all "I'm not ready yet, it's too hard/risky/expensive/[insert thing here]." It ends up being, "Well s**t-I totally could've done it and who knows-maybe I'd be better off than now." I'm not even going to count all the trends I didn't cash in on because I was too afraid to try.
Not that there's any way of knowing if any of it would've worked out. I gotta stay in the present more, not that I'm good at that as I'm still lamenting bad decisions I made as a teenager despite being 26.