At some point or another, nearly every sci-fi/fantasy show does their own version of Groundhog Day. But few shows give the idea of reliving the same day over and over again the level of emotional resonance that "Mystery Spot" possesses. In the beginning, watching Dean die over and over in increasingly ridiculous ways is weirdly funny, but things turn serious as the cycle continues to a point where Sam's desperation to save his brother is palpable.
Like all of the best monster-of-the-week episodes, "Mystery Spot" leans into the Winchester brothers' connection, but this episode shows a more devastating side of their bond: an inability to let go of one another, no matter the cost.