Gaze-based interaction in Virtual Reality (VR) has been attracting attention recently due to rapid advances in eye tracking technology in head-mounted displays. Since gazes are a natural and intuitive interaction modality for human beings, gaze-based interaction could enhance player experience in immersive VR games. Aiming assistance is a common feature in games to balance difficulty for different player skills. Previous work has investigated different aim assistance approaches and identified various shortcomings. We hypothesize that "bullet magnetism" is a promising technique for VR and could be enhanced by extending its functionality through players' gazes. In this paper, we present a gaze-based aiming assistance approach and propose a study design to evaluate its performance and player experience in a "Mexican-style" VR first-person shooter game.