A rogue Rammerhead instance can inject its own JavaScript into every page you load. This script could:
Rammerhead allows you to create a persistent browsing session. When you access your session, your localStorage and cookies are synced across visits, making it possible to stay logged into websites and retain your settings even if you switch devices. rammerhead proxy list link
Using a public Rammerhead link from a "proxy list" carries significant risks: A rogue Rammerhead instance can inject its own
Rammerhead Proxy is a high-performance web proxy built on the testcafe-hammerhead rammerhead proxy list link
binary-person/rammerhead: User friendly web proxy ... - GitHub