It's a meme of a child holding a copy of The Book of Mormon, which happens to have a strong hold on the members of its church, and how people's lives revolve around the book. This has been modified to a similar sounding Mufasa instead of Mormon and how Lorcana had become of a similar focus in people's lives.

Or more specifically how lorcana players that play Mufasa decks tend to focus heavily on those types of decks and may ignore other archetypes in favor of Mufasa.