Cosmic Motifs: According to the official guidebook, Elfilin's ears were designed to resemble the waxing and waning of the moon. This was meant to represent "having lost the quality of a single existence", that is, having separated from Fecto Forgo.
The Fog of Ages: According to the official guidebook, he barely has any memory of his time as a test subject in Lab Discovera anymore.
Based on machine translations, the TV Tropes descriptions seem pretty accurate. And according to a commenter on the original Reddit post, in the Kirby light novels (separate continuity from the games, so take the implications with respect to game canon with a grain of salt), Elfilin also doesn't remember Lab Discovera. So that's some not-so-new-at-this-point-but-still-not-widely-talked-about Elfilin lore for you.