Paleontologically speaking, Gnar is not a missing link, i.e. transitional specimen, but he belongs to the Yordle population ancestral to modern ones; colloquially-speaking, he is the great-great-...-granduncle of all living Yordles.
In Brazilian localization Gnar's title was changed to O Yordle Pré-histórico ('the Prehistoric Yordle') in order to avoid matchmaking-rating-associated jokes/bullying derived from O Elo Perdido ('the Missing Link').
Gnar is the second champion to have two champion portraits (Mini Gnar and Mega Gnar) the first being Quinn and Valor.
He is also the third to have more than one chat name, the first being Anivia and Eggnivia and the second being anyone polymorphed by Lulu (Squill).
He is unaware that he transforms but that may change when he grows older.
He retains his personality as Mega Gnar.
The tribal paintings in 'Discovering the Link' depict Gnar and his family living in peace until a one-eyed entity with two horns/tentacles (speculated to be a Frozen Watcher or one of Vel'Koz's Voidborn species) attacked them. It knocks Gnar's family away, triggering his Rage Gene therefore turning Mega, and promptly fighting the entity to unknown success.
Apparently defeated Anivia encases Gnar for centuries in True Ice to preserve him and ultimately awakens him again to fight the Frozen Watchers on the brink of their return.
Immediately after his escape he's rampaging through the woods as Mega Gnar, with Rengar hunting him down to take him as a prize.
Gnar learned to use a boomerang from and fashioned his after his father's.
The boomerang is hidden in Mega Gnar's fur when he transforms.
Gnar is the only Yordle in modern times to have a tail due to his antiquity.
What appears to be childish babbling is actually Gnar's own native language.