This mixed-methods study investigated the prevalence, impacts, and determinants of mood fluctuations and egodriven behaviors among research supervisors in Ugandan universities. A convergent parallel design was employed, involving a cross-sectional survey of 384 postgraduate students from five purposively selected institutions, complemented by 15 in-depth interviews, 12 key informant interviews, 6 focus group discussions, and document analysis. Quantitative data were analyzed using univariate statistics, bivariate correlations, independent t-tests, and structural equation modeling to examine relationships between institutional factors, supervisor behaviors, and student outcomes. Results revealed that 75.3% of students experienced mood fluctuations and 80.5% encountered ego-driven behaviors from supervisors, with intellectual superiority displays (84.9%) and inconsistent emotional responses (81.3%) being most prevalent. Public universities exhibited significantly higher levels of both behavior categories compared to private institutions. Bivariate analyses demonstrated strong negative correlations between supervisor problematic behaviors and research progress (r=-0.58 to -0.62, p