Some modern unblocked gaming portals use JavaScript-based console emulators (like JSnes or specialized PS2 web ports). If you find a functioning unblocked site, the game will load a ROM file directly inside your browser window.
This game introduced the famous slow-motion targeting system. Players slow down time, paint targets on enemies, and release a volley of precise shots.
So why are you seeing "unblocked" versions? Many sketchy sites use the name "Red Dead Revolver Unblocked" as clickbait, but they actually give you: