Gary Synthesizer is the 23rd episode of season 7 of Regular Show.
Mordecai and Rigby accidentally reset Gareth's synthesizer, causing him to vanish.
Skips is called by his friends Gareth and the Guardians of Youth to join a Guys Night in the galaxy, with Skips refusing due to needing to cleaning his garage with Mordecai and Rigby helping. While the duo are cleaning the garage, they spot a synthesizer and decide to mess the thing around. However, Skips warned the duo that thing is Gary's synthesizer and suddenly Gareth's car crashes with only the Guardians of Youth inside. They explain that Gareth disappeared while driving in space, causing their car to crash (since the Guardians don't know how to drive). They also explain that the synthesizer projects Gareth's physical form and that by messing with its cables and plugs, Mordecai and Rigby vanquished it (though he isn't dead, his consciousness still resides in the synth). They try in vain to put its plugs back the way they were (only succeeding in making it produce a high-pitched noise that destroys Skips' priceless glass harmonica).
The Guardians then teleport them to Gareth's home world of Synthos in order to recreate the original patch. They arrive in Synth city (with buildings and structures that resemble various electronic instruments) and are almost immediately greeted by the planet's king and ruler David. Rigby claims to be the king of earth (Mordecai hits him with the synthesizer) and David greets them as "ambassadors" of Earth. He offers to take them to his office. On the way there he explains that all citizens (referred to as "Synthizens") play music in perfect harmony. He sees two Synthizens, whose names are Robert and Keith, play in discord and immediately deploys a robot to arrest them. He takes them to a large Pyramid-shaped building called Hymn Hall which contains holographic heads of Synthos' previous rulers (himself last, and the one before him missing). At his office Skips shows him a picture of Gareth (which he seems to recognize) and he takes them to a "re-synthesizing studio".
It is a platform-like room encased in a glass-like pyramid shell with a door. Robert and Keith, who David arrested earlier, are also in the studio. He then seals the door, trapping all five of them in the studio. He claims that Gareth is Synthos' most wanted criminal. Supposedly Gareth's "experimental jam sessions" nearly destroyed the planet and that they are associated with him, thus making them "criminals" themselves. He then tells them that they are going to meet the same fate as all criminals of Synthos (referred to as "discordants"): they will be launched into the planet's sun called the Synth Star. After failing to penetrate the studio's walls, the two discordants tell them its futile and that the walls are made from "futuristic material" (called tempered glass on Earth). Remembering the synthesizer's ability to destroy glass, Skips has Mordecai and Rigby rearrange the cables again, causing it to emit the same high-pitched noise from earlier and destroy the studio's walls. This time, the synthesizer briefly projects an angry depiction of Gareth before becoming idle again.
Robert and Keith (and the surrounding Synthizens who came to watch the execution) recognize the synthesizer as Gareth's and reveal that he is Synthos' true ruler. They reveal (through holographic depictions) that after Gareth vanished 200 years ago, David seized his throne and completely outlawed "challenging" music. Mordecai and Rigby recognize the patch from the projection. David, now exposed, deploys two more robots to stop them from re-synthesizing Gareth. Mordecai and Rigby work on fixing the patch while Skips holds off the robots. They finally succeed and Gareth is re-synthesized back into his physical form. David is also revealed to be Gareth's half-brother and he challenges him for the right to the throne. The two proceed to have a battle using both the synthesizer and a holographic keyboard generated by David.
Gareth ultimately wins by playing a discorded note perfectly (something David viewed as impossible) and blasting him onto the studio, which then launches into the Synth Star, destroying his body. Robert and Keith then destroy David's synthesizer, killing him for good. Mordecai and Rigby question this and Skips tells them that it's just the way of Synthos. Gareth ultimately prompts to not be Synthos' ruler and steps down from the throne, telling the Synthizens to let music guide them for the rest of their days. Mordecai and Rigby apologize for the whole mess and Gareth tells them rock stars have no need for apologies and promptly summons his car (with the Guardians of Youth inside impatiently asking if they can finally go to the mall).
- Rigby's tail briefly disappears towards the end of the episode.
- The discordants names are Robert and Keith, which were revealed in the episode's credits.