BLUE (more commonly known on the internet as Blue/Green Mother-Fucking Oak) is RED's rival, and he appeared as the main antagonist in Twitch Plays Pokémon Red Version.
BLUE's in-game sprite
Role
Throughout Twitch Plays Pokémon Red Version, BLUE would appear in certain places to do battle with RED, always scoffing at his battle skills. Despite BLUE's ego, he always managed to lose to RED.