Probably inviting Whitney from my campsite to my town, which I never should have done in the first place. She stayed in my town for 9 months before leaving my town. The only good thing that came out was that I got a lot of bells for her when she moved out.
When I had my town all finished and a villager moved out and Jambette moved in a ruined my entire town. While trying to get her out I lost several villagers I liked. I reset :c
Actually, that's probably the thing I hate most about the game. It shouldn't be a time consuming game, but it is for me because I'm super anal about my town. Also, I wish faces, player/town names, and villager plots could be modified/chosen. Those things alone would save a lot of frustration and time. LOL!
But in terms of actual activity in the game itself, I once had Marshal in my campsite. I time traveled too far, and he moved into a bad spot. :'-)
This one is a hard one to answer though. But I can say that some animals I didn't take too much care of moved away too soon when I was time traveling back and forth for the paintings.
My favorite villagers moving was probably the worst thing, but now it's just like eh it happens.
I used to spend way too much time on the game so that's kinda bad too lol. was a complete addiction.
Failing plot resetting...three times ;-;
Ended up with Francine in front of Brewster's, Octavian near the cliff, and Marshal in a place where I originally wanted to put a PWP.
My 1st town the obvious answer is it corrupting the day I finally got Lopez. - and subsequently in my 2nd town not liking him very much because of this.
My 2nd town would be when I first made it I wanted to get the shops opened up quickly and TT'd the first month or so. During this I had Beardo move in while plot resetting because I didn't check that small gap infront of another villagers house. And then a few hours later completely forgot to plot reset for a Marina I'd just adopted and she crushed my hybrid garden directly infront of my house. I was so peeved, and had to let her move out because of her awful placement.
And my brand new town ~ like a day old. I created during the early hours of the morning, slept for a while and left it on and then awoke to 6AM passing and Renees house plot appearing. S: Though am fine with her and the placement, it's a bad start to the town for me.
Before I figured out decent strategies for time-traveling, I was really careless with how I did it (or more accurately, I thought I was being careful, but it turns out I didn't quite know how it works). As a result, I ended up losing both Whitney and Julian before I figured out how to do it properly.
Accidentally dug up a Jacob's Ladder next to a fossil spot the other day, and I was so far into my routine that I couldn't possibly reset :/
That, and Olivia leaving town when I took a one week break when Omega Ruby/Alpha Sapphire came out... if only those games were good I could've at least left the experience with something, but no. Olivia tried to warn me!