"Path of Achra" for a pretty traditional roguelike that focuses on short runs and setting up "broken builds". Highly rated and pretty cheap.
"Halls of Torment" It's vampire survivors x diablo. My favorite of the genre beside the "original". Not sure how hidden it is though.
"Stone Story RPG" Not really sure how to describe this one. ASCII art sorta-idle game?
"Siralim Ultimate" mystery dungeon type monster rearing rpg with some wild synergies and buildcrafting. Tonnes of ways to "break the game"