Errant is a massive rework of an old comic of mine called Fan Dan Go. Which is actually still up over on The Duck. There was about a nine year gap in between running out of steam on FDG and starting Errant, with a lot of times in-between where I was like "...should I continue FDG?"
There are a lot of changes to Errant, many of them addressing issues I had with my comic like "needs more diversity" and "Okay turns out I'm gay, I want to reflect that in the themes of my story", and then issues readers had, like that the 1970s British setting, complete with a lot of Northern English slang, was alienating to readers, there wasn't a strong villain or stakes etc.
A big, central change to Errant from Fan Dan Go, is the addition of Arthurian legend stuff. It feels weird to think that this wasn't in FDG, because it's pretty much the central basis of the whole plot in Errant. It was such an obvious way to both add a strong core conflict, and to make it something that's definitely very British, but also that a broad, international audience could get into; everyone knows Excalibur is an important magic sword, and that the King who wields it lives in Camelot and has a round table and knights. People understand the significance of pulling Excalibur out of a stone and becoming King (and yes, lore buffs, I know that actually it wasn't Excalibur that was pulled from the stone in the legends, it was a different sword and might have been an anvil etc. etc.), so it was really convenient. Then rather than having Jules' brother be dead, I had him as the main villain, because Jules was the most popular character even back in FDG, but was really the least plot relevant, one, so I shuffled things to make them actually vital to have around.
All in all, it took a lot of planning, but I think Errant is so much better than Fan Dan Go was. I definitely spent months just writing out all the lore, and basically everyone is redesigned to at least some extent. I did a lot of historical and mythical research too to make the whole thing feel fleshed out, and even put a lot of time into renaming it, from a name I came up with on a whim as a teenager that basically means nothing, into what I consider to be a much more fitting title!