I like how Strange Memories of Death is the Megalovania of Gimmick!, except instead of being for a super hidden badass event that most people won't realise is even in the game, it really is just actually not in the game
Trying to think of other small platformers with the same mysterious tone as Gimmick / Trip World that aren't Kirby's Dream Land 1… This may be shocking considering how much text it has, but my top candidate might actually be Kero Blaster.