The Karl Effect refers to a persistent internet theory and meme regarding Karl Jacobs, a prominent member of MrBeast’s crew and the Dream SMP. The term originated within fan communities to describe the perceived shift in content style or group dynamics following his arrival, ranging from criticism of a changed 'vibe' to praise for his unique energy. While often used to spark debate among YouTube audiences, the meme has evolved into a broader template for discussing any situation where a single new person or element fundamentally alters the chemistry of an established group. On memeOS, creators use this template to highlight 'before and after' scenarios, often contrasting a chaotic or serious past with a more colorful or whimsical present.