Team 0% is attempting to clear every level in Super Mario Maker before the servers shut down on April 8. (New level uploads have been disabled since 2021, so there is no danger of new levels appearing at the last minute.) As of a few days ago, only a single level remains: Trimming the Herbs, uploaded in 2017 by Ahoyoo. (See also Ahoyoo’s original upload video.)
The level is short but extremely precise, requiring Mario to use Bob-ombs to precisely remove Piranha Plants and collect coins while navigating a tight space filled with spikes. There have been over 200,000 attempts so far! If you have a Wii U and feel like you might be a Mario master, this is your opportunity to pick up the final First Clear in Super Mario Maker history.
I know I’ve seen “cryptographically secure” levels (as in, you can only possibly beat it within a human lifespan if you know the specific “combination” or “cryptographic key”), but maybe only in Super Mario Maker 2.
And I’m not sure if in 1 you can inspect the whole level. The SMM2 cryptographically secure ones I’ve seen rely on mechanisms that must remain off-screen the whole time or else it’s trivial to derive the key.
It’s only in SMM2, which doesn’t allow you to edit other people’s levels. And actually there is now a 3rd party tool to view SMM2 levels so those levels are now exposed as well.