The phrase "Sigma Boy x Evolution of Brainrots" refers to a mashup or remix that combines the "Sigma Boy" meme/song with the "Evolution of Brainrot" meme series.

Sigma Boy: This refers to the popular song by Russian child stars Betsy and Masha, according to YouTube. The song is associated with the "Sigma male" archetype, which portrays a man as independent, self-reliant, and living outside traditional social hierarchies. The song became a viral sensation, especially on TikTok, where users create humorous videos featuring a sped-up version of the track, often incorporating dance animations and gaming references.

Evolution of Brainrot: This refers to a series of internet memes featuring absurd and often AI-generated creatures with pseudo-Italian names, accompanied by synthesized voiceovers and nonsensical narratives, according to Wikipedia. These memes gained popularity due to their surrealist humor and the catchy, repetitive phrases associated with the characters, leading to a phenomenon where viewers might find themselves humming these phrases days later. This type of low-value, repetitive online content is often described as "brainrot," a slang term referring to the mental decline that can come from overconsumption of such content.

Sigma Boy x Evolution of Brainrots: This combination blends the themes of the independent "Sigma male" archetype with the absurdity and catchiness of the "brainrot" memes. It often results in music videos and animations that feature the "Sigma Boy" character interacting with or transforming through various "brainrot" creatures and elements.

Essentially, the combination is a reflection of current internet culture, where popular memes and trends are often remixed and mashed up in creative and humorous ways, sometimes to the point of being labeled as "brainrot" due to their nonsensical or repetitive nature.