The episode introduces "solids," a game where one person must immediately fulfill a favor for the other. Despite a warning from that abusing the power of solids will cause "bad things to happen," Mordecai and Rigby ignore him to settle petty tasks.

In the Regular Show episode (Season 2, Episode 18), a casual game of favors escalates into a supernatural catastrophe. The episode is well-remembered for its exploration of the friendship between Mordecai and Rigby and its famously ambiguous "tenth solid" "Do Me a Solid" | Regular Show Wiki - Fandom . Plot Summary: The Danger of "Solids"

The stakes rise when asks Rigby on a double date with Mordecai and Margaret . Desperate for a chance with Margaret, Mordecai begs Rigby to "do him a solid" and go. Rigby agrees but demands Mordecai owe him ten solids in return, which he then uses to systematically sabotage Mordecai's date through increasingly embarrassing tasks. The Infamous "Tenth Solid"

The episode's climax occurs when Rigby demands a final, extremely humiliating tenth solid in front of everyone. When Mordecai initially refuses, the park house begins to physically break apart, fulfilling Skips' warning. Mordecai eventually performs the favor to save everyone, but the actual act is never shown to the audience. "Do Me a Solid" | Regular Show Wiki | Fandom