Here's why:
* Mordecai's Sacrifice: Mordecai willingly sacrifices his ability to talk to animals to save Rigby from a dangerous situation. This loss is deeply personal and significant to him, as his connection to animals was a defining part of his character.
* Rigby's Guilt: Rigby is left feeling overwhelmed with guilt for putting Mordecai in that position. He realizes the depth of Mordecai's sacrifice and struggles with the weight of it.
* The Emotional Impact: The episode is beautifully done, showcasing both the pain of loss and the strength of their friendship. The final scene where Mordecai looks at Rigby with a sad smile and nods his head, signifying he wouldn't trade the experience for anything, is truly heart-wrenching.
Other contenders for the saddest moment could include:
* "The Date" - The episode where Pops attempts to move on from his ex-girlfriend, showing the heartbreak of unrequited love.
* "The Power of Nothing" - The episode where Mordecai and Rigby are forced to confront their fears and insecurities.
* "The Power of Love" - The episode where Mordecai and Rigby learn the importance of friendship and sacrifice.
Ultimately, the saddest moment in Regular Show is subjective and depends on what resonates with each viewer. But "The Power" stands out for its raw emotional impact and the depth of the characters' sacrifice and growth.