Streamer plays SMB3 (or similar NES game) using the BizHawk Real Time corruptor mod.
Hotkeys are mapped into various RTC functions, by a bot that hangs out in the twitch chat.
One random viewer is chosen. They have 30 seconds to !roll a d20 equivalent, which determines how many rounds of garbage are injected into the game. Other methods to get extra injections include trivia and puzzles.