I hope I answered your questions. For the biggest writing mistake, did you mean specifically my Destiny stories or my creative writing in general? If it's the latter, it would be creating a character that was too cliche and overdone (though it wasn't as overboard as most fanfic writers go), though I've honestly always been pretty good about keeping characters realistic.

Survivors biggest mistakes: I kind of regret writing in first person, but it's alright since I didn't change perspectives. Book 2 will be third person with changing perspectives. I started posting Survivors before I had completely solidified my idea of how the Vanguard and City Military would work, so the first two chapters are slightly inaccurate. There are several instances where I tried inserting backstory in conversation, and it seemed forced.

Blank Slate biggest mistakes: Writing in first person, because it's an absolute nightmare when I use changing perspectives. Trying to create an exact timeline with specific dates. Not exactly a mistake, but I do regret trying to focus on Keis's past life

Silliest custom game idea: I don't know the extent of the customizations, so I'll just say Mayhem Rift, because it would be nearly impossible to deliver the Rift