what is the idea behind that statue?

[Sheep]

So the smirking statue lets you trade your locusts to jump some floors ahead.
And then there is a black statue, and when when I put the exit in front of it and exit it writes "all that remains..." and brings me back to the first floor...

is that a restarting statue? does it do anything else other then that?

In one of my runs I accidentally got into some room that gave me a cube, and after that I could read murals but i dont know how i did it or how to recreate it.

I thought it might be related to that statue but after restarting few times already I figured out not.

[SleepyKitsune]

that black statue resets you back to the first floor without any locusts, in some situations its in places to make you mess up and accidentally reset yourself, other then that, doesnt do much but get in the way

[Lily]

The black statue also removes void status, which may come in handy.

[zyrax]

yea i discovered this in an...interesting way.