Future Mordecai & Rigby are Future Version of the main character from the Regular TV series.
Those two are Mordecai and Rigby's future counterparts who appeared in "Mordecai and the Rigbys". In the future, they were millionaire singers and had all the things they ever wanted (Future Rigby had a shark tattoo on his armpit and Future Mordecai might have finally dated Future Margret). They also pretend to have British accents like the One Direction band and never take their sunglasses off.
They appeared when Mordecai accidentally spilled a can of soda on some record players. Future Mordecai and Future Rigby taught their younger selves how to play the instruments in a good way, although their learning didn't progress well. On the night of the show, Mordecai and Rigby do surprisingly well while singing Party Tonight, that is until Mordecai realized they were lip-syncing because the guitar music and the lyrics he and Rigby were signing came only from the CD.
Mordecai and Rigby decide to stop what they were doing and refused to make their way to fame through means of lying and fraud. The two then remove their t-shirts and break up the band which causes their future selves to vanish.
- They are the reason Past Mordecai didn't trust Mordecai and Rigby in "Bad Kiss."