Heh. You gotta endure the stairs as a pre-challenge!
The basement's so much smaller than the Easy Mode lobby! Interesting! Probably not boss-refights, that's not really a challenge? That's also not unique.
Lol if it's not fighting but is instead puzzles.
There's no Point Redemption Station here, so rewards are different?
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Boss refights would probably come later, after the Main Story. And I'd do it in a manner similar to the "Boss Endurance" mode in Kirby's Adventure/Nightmare in Dream Land that I could never beat when I was a kid. (I always choked at Meta Knight or Dedede.)
You still get the same Tower Points, and the rewards upstairs will update accordingly, but there also might be some unique rewards in this challenge depending on different "high scores" in the challenge. I'll have to think about it!