Previous research has highlighted the unique challenges young Autistic adults face when using social media. We extend this work by analyzing how guardians and allies, such as service providers, mediate the social media usage of young Autistic adults in order to address and mitigate online risks. Based on analysis of interview transcripts (8 young adults on the Autism spectrum, 4 parents, 10 staff members), we uncover the mediation tactics used, how they differ based on the ally's relationship with the individual, and the tactics' varying degrees of effectiveness. The findings of this research contribute to the literature by informing the design of technology to facilitate more effective mediation, and identifying the need for improved digital literacy and opportunity for curriculum-based mediation.