Harassment, especially of marginalized individuals, on networked gaming and social media platforms has been identified as a significant issue, yet few HCI practitioners have attempted to create interventions tackling toxicity online. Aligning ourselves with the growing cohort of design activists, we present a case study of the GLHF pledge, an interactive public awareness campaign promoting positivity in video game live streaming. We discuss the design and deployment of a community-driven moderation intervention for GLHF, intended to empower the inclusive communities emerging on Twitch. After offering a preliminary report on the effects we have observed based on the more than 370,000 gamers who have participated to date, the paper concludes with a reflection on the challenges and opportunities of using design activism to positively intervene in large-scale media platforms.