Problem
I wanted to build something that would actually spread on its own at school, not just something I'd show people.
What I built
A gacha card game where the cards were generated from real Outlook profile pictures pulled from the school directory. There was no marketing for it. It spread entirely by word of mouth within a few days.
Hardest part
Pulling the directory photos in a way that actually worked reliably, since the Outlook API was not built for this and the photo availability was inconsistent across accounts.
What I'd change
Nothing about the build, honestly. It resulted in a formal warning from the school. Still worth it. In hindsight, though, I should have been more careful with privacy. Using real people's photos without asking them wasn't right, even if it was technically possible.