Honestly, I am not 100% sure about this part... but other guides indicate it as a pre-requisite.

If you use Faily you can see all secret rooms in a level/zone.
In the level with Nibble's secret room you will see two secret rooms instead of a single one.


If you want to unlock Faily you can check my other guide:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2435653360

This character is available only if you have Rogue Glitch Ultra (so not the old Rogue Glitch).