Lemmy Koopa did not originate from fanon, and more information can be found on their respective wiki(s). You may read more about it on the following wiki(s):

Lemmy Koopa (known as Hip Koopa in the cartoons) is the second oldest and smallest of the original 7 koopalings. He is often associated with child-like traits due to his personality, size, and behavior. He is known for is multicolored mohawk, lazy eyes, and his rubber ball, which he is often seen balancing on top of. He is able to cast rubber balls from his scepter as well. Lemmy was named after Lemmy Kilmister, who recently died, from the band Motörhead.

Personality AUs

In Aiva's AU of Lemmy, he is the 2nd oldest, being bisexual. He loves Ludwig, and Ludwig loves him. Lemmy is quite smart, as he is a Senior in high school. Lemmy is 18 years old, born on April 21, 1998. He, Iggy, and Ray are siblings, and their father is named Remmy.

In [Luxa]'s AU of Lemmy, Lemmy is the 2nd oldest out of the koopalings (thought to be the youngest). He has a playful and fun-loving behavior in general, but when fighting, he can be serious & difficult against his opponent(s). He has the closest relations with [Larry Koopa]. Lemmy is thought to be born sometime in the early 1980s.