100% confused on Chaos Malachite

[Meadow Daydream]

In order for me to get this I have to reach to minute 18:00 in Bat Country.

But I don't have Bat Country.
Looked it up I need to reach level 80 in Inverse Mad Forest.
How do I get Inverse? LOOKED THAT UP! Uggggh.

Says I need to collect a Relic known as Gracia's Mirror.
Looked that up says I need to go to Eudaimonia.

Now this is where I am confused.
I collected every base game relic and got to Eudaimonia. I was given the options "Too Easy" and "Too Hard"

Me not even bothering to look it up I selected Too Hard. And I have unlocked "Endless mode"

This was a while ago.
So It's only until now that I really need "Inverse Mode"
How do I go back to Eudaimonia to claim the other Relic? "Gracia's Mirror"

[SunderedSalmon]

The stage reappears once you've played a game with the new gamemode. You can probably just quit immediately once you've entered the stage, it should appear after that.