BrainForm is a P300 event-related potential (ERP) EEG dataset collected from 22 participants using a gamified brain-computer interface (BCI) designed for scalable data collection with consumer hardware. Participants completed repeated runs of a P300 spelling/selection task within a serious game paradigm, enabling investigation of BCI skill acquisition across sessions and perceptual effects of different visual stimulation textures. The dataset supports research in BCI training, human factors, and machine learning applications on ERP data.